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What Heresy Is—and How to Guard against It

The history of the Christian Church is riddled with teachers whose work looked and sounded like orthodox Christianity—but wasn’t. Sometimes their teaching was so close to Christianity that it was hard to tell the difference.

The same is true today.

As twenty-first-century believers in a world full of uncertainty, it’s as important as ever to know how to spot an error in teaching. There’s so much theological “noise” that we must train our spiritual “ears” to know when someone’s teaching is not biblically sound.

But that is often easier said than done.

Below we’ll unpack the topic of heresy—what it is, if it’s in the Bible, what some of the main heretical movements were in Church history, and more. You can start from the top or skip to the topics that interest you.

What is the definition of heresy?
Is the concept of heresy in the Bible?
How to know what’s heretical
Heresy in the early Church
Why the topic of heresy matters
Why we must guard against heresy

What is the definition of heresy?

Before diving into the specifics of how to spot heresy and whether Christians should study it or not, let’s first define a few terms, starting with “orthodoxy.”

The Dictionary of Christianity in America defines orthodoxy as “beliefs judged to be essential to Christian truth.” The word comes from two Greek words, orthos and doxa, which literally mean “right opinion.” Over time, orthodoxy has come to refer to “established beliefs or doctrines.”1

Simply put, orthodoxy is “right belief.”

Heresy is its opposite. Merriam-Webster defines heresy as “adherence to a religious opinion contrary to Church dogma [doctrine] or to generally accepted beliefs or standards.2 The original Greek word was hairesis, and in ancient biblical times, could be used to refer to philosophical schools or “sects” of the Greek world.

Heresy is not interpretive error but an outright choice to turn against the established doctrines of the faith and follow a different, personal view. Such a view can rise all the way to the damning level of “preaching another gospel,” as Paul mentions in Galatians 1:9:

As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you received, let him be accursed. (Emphasis added)

However, the definition of heresy gets muddy quickly. New Testament scholar Michael F. Bird says that what a church believes doctrinally may define one person or group as “heretical” while another church does not.3

So how do we know if a teaching is really heretical?

Let’s first see what God’s Word says about it.

Is the concept of heresy in the Bible?

The Greek word hairesis appears nine times in the New Testament, and it often refers not to especially erroneous doctrines but to religious sects—groups characterized by distinct opinions, teachings, or practices.

Twice in Acts there are references to the hairesis of the Pharisees (15:5; 26:5), and once to that of the Sadducees (5:17). Clearly, here, the best English translations of the word are “party,” “sect,” or “faction.”

Though hairesis (heresy) initially meant different factions, Michael Bird says that over time it came to mean “deviating from established doctrine in major areas like the Trinity, Christology, and soteriology.”4

And those who did so became known as heretics,5people whose teachings, according to Bird, “the Church at large considers erroneous and even dangerous to the faith.”6

Of course, a person was not heretical just because the Church deemed it so but because their teaching abandoned what Paul called “the pattern of sound teaching” (2 Tim 1:13 NIV).

The Christian religion gets called a hairesis in Acts too. Once it’s called this by critics (“the sect of the Nazarenes,” Acts 24:5). Once it’s called this by Paul reporting the words of critics “the Way, which they call a sect,” Acts 24:14). But once Christianity is called a hairesis by Roman Jews who are open-minded (Acts 28:22), making it unlikely that the word had a universal negative tone. Think of “religion,” which is positive, versus “cult,” which is negative; hairesis probably leaned toward the former—or perhaps it was a neutral designation.

The Logos Bible Word Study shows the different ways that the Greek word hairesis gets translated in the New Testament:

The Jewish historian Josephus used hairesis in this basically neutral way when referencing the Pharisees, Sadducees, and Essenes,7 three prominent sects in Jesus’ day. (And according to the International Standard Bible Encyclopedia, first-century Jewish rabbis used the Hebrew equivalent the same way.)

In this sense, a hairesis is not necessarily a flagrant violation of orthodoxy. It wouldn’t do to translate any of the uses of hairesis in Acts with the English word to which it gave rise, “heresy.” To do this would not fit the contexts; it would actually be to commit the etymological fallacy: just because “heresy” came from hairesis doesn’t mean that hairesis meant “heresy” 2,000 years ago.

But listen to the way the apostle Paul later uses hairesis in his letters. He assumes that a hairesis is bad, even placing it on a vice list. He uses the word to refer to unhealthy divisions among believers—though still not necessarily to especially erroneous doctrines:8

When you come together as a church, I hear that there are divisions among you. And I believe it in part, for there must be factions (hairesis) among you in order that those who are genuine among you may be recognized. (1 Cor 11:18–19)

Now the works of the flesh are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions (hairesis), envy, drunkenness, orgies, and things like these. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God. (Gal 5:19–20)

In these contexts, the word is picking up the flavor it will eventually come to have, but it isn’t there yet. Paul never says that the “parties” that claimed, “I am of Paul,” “I of Apollos,” “I of Cephas,” and “I of Christ” were holding different doctrines. They were, instead, adopting heroes who had become symbols, banners, boundary markers. Paul saw the devastating impact these divisions could have on the fledgling Church—and he fought vigorously against any developing hairesis among his precious baby churches. (Paul’s first recorded words in the Bible rebuked a man named Bar-Jesus in Acts 13:4–12 for false teaching: “Will you not stop making crooked the straight paths of the Lord?”) Paul knew it was critical for the young Church to remain united.

By the time of 2 Peter, hairesis may have come to mean something more like our heresies. The context could still support the translation “factions,” but Peter’s focus is on teaching, on doctrine—and he names one central and essential doctrine that is a hairesis to deny:

But false prophets also arose among the people, just as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Master who bought them, bringing upon themselves swift destruction. (2 Peter 2:1 ESV)

Resources about heresy you may be interested in

Mobile Ed: TH200 Christian Thought: Orthodoxy and Heresy (8 hour course)

Mobile Ed: TH200 Christian Thought: Orthodoxy and Heresy (8 hour course)

Regular price: $299.99

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Heretics

Heretics

Regular price: $9.99

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Know the Heretics Video Study

Know the Heretics Video Study

Regular price: $89.99

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Mobile Ed: CH351 History of Heresies (7 hour course)

Mobile Ed: CH351 History of Heresies (7 hour course)

Regular price: $259.99

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I Call it Heresy: And other Timely Topics from First Peter

I Call it Heresy: And other Timely Topics from First Peter

Regular price: $11.99

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Early Church History Collection (7 vols.)

Early Church History Collection (7 vols.)

Regular price: $99.99

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A Messianic Commentary: From Jude on Faith and the Destructive Influence of Heresy

A Messianic Commentary: From Jude on Faith and the Destructive Influence of Heresy

Regular price: $9.99

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The Cruelty of Heresy: An Affirmation of Christian Orthodoxy

The Cruelty of Heresy: An Affirmation of Christian Orthodoxy

Regular price: $17.99

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How to know what’s heretical

The danger of heresy does not mean Christians can’t differ on any theological questions whatsoever. According to Beth Felker Jones in her course Christian Thought: Orthodoxy and Heresy, there are differences among Christians that are sometimes called adiaphora, or “indifferent things.” Felker Jones teaches that yes, theological differences matter, but we must allow space for people to “live and let live.”9

Take, for example, whether infant or believer’s baptism is best. Jones writes:

People are very committed to their views on one side or the other, but most of us recognize that our brothers and sisters who disagree with us—who are on the other side of that practical divide—are still Christians, are still in the faith, and are still in Christ, although we may be convinced that they are quite misguided. There are no major heresies related to whether you baptize infants or believers, at least not ones that are shared across the whole of the Church.

And so orthodoxy and heresy as categories, Jones says, “help us to think about truth and falsehood”10 and act as a protective hedge for believers.

Know God’s Word

The best guard against being swept away by false teaching is to know God’s Word and know it well. This requires more than a cursory read, which can still teach and inspire us but won’t help us understand deeper concepts better so we can distinguish truth from error.

The apostle Paul understood that handling God’s Word appropriately takes effort:

Do your best to present yourself to God as one approved, a worker who has no need to be ashamed, rightly handling the word of truth. (2 Tim 2:15, emphasis added)

Handling God’s Word responsibly is our job, our task as believers—especially if we’re teaching others. (Using tools like Logos is invaluable for being able to do this well—more on this below.)

See how Logos can help you research any word or topic.

Heresy in the early Church

In the early centuries of Church history, pagan philosophies impacted Christianity’s foundational beliefs. Justin S. Holcomb, the author of Know the Heretics (part of the Zondervan Know Series 4 vols.), writes that “many of the heresies that arose had to do with the identity of Jesus Christ as he related to the God of Israel.”11

According to New Bible Dictionary, the two most prominent heresies in the New Testament were a Jewish variety of Gnosticism (Col 2:8–23; see below) and Docetism (1 John 4:2–3; 2 John 7; see below). However, other heretical movements developed in the first few centuries of Church history. Click to explore them all, or jump to what interests you:

Judaizers, 1st century AD

Heretical belief: First-century Jewish believers in Jesus who attempted to impose Jewish laws and way of life on gentile believers. The word “Judaizer” shows up only once in the New Testament, in Galatians 2:13 (“follow Jewish customs” in the NIV and “live like Jews” in the ESV and NASB), and it means “to live according to Jewish customs and traditions.”12

What the Bible says:

“For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.” (Eph 2:8–9; see also Acts 15:4–12; 23–29; Gal 2:16)

Implication: If salvation is dependent on what a person does, there is no need for a Savior.

Docetism, late 1st century AD through AD 35

Heretical belief: Jesus only appeared to be human—he did not have a physical body13 and was therefore not a man.14

What the Bible says:

“And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.” (John 1:14; see also John 20:7; 1 John 4:1–3)

Implication: If Jesus was not human, then he did not die for the sins of humanity and we are still in our sin.

Gnosticism, 2nd century AD

Heretical belief: A person can only obtain salvation through revealed knowledge, or γνῶσις (gnōsis).15 Gnostics also held a negative view of the physical or material world. 

What the Bible says:

“Timothy, guard the deposit entrusted to you. Avoid the irreverent babble and contradictions of what is falsely called ‘knowledge,’ for by professing it some have swerved from the faith. Grace be with you.” (1 Tim 6:20–21; see also Col 2:8; 1 John 4:2)

Implication: If a person can only obtain salvation through revealed knowledge, Scripture is unreliable.

Marcionism, 2nd century AD

Heretical belief: An angel created the material universe by accident; the God of the Old Testament and Jesus of the New are two different gods—a creator and a redeemer. The OT Scriptures are deceptive and should be rejected.16

What the Bible says:

All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness.” (2 Tim 3:16, emphasis added)

Implication: If there are two different gods, then the gospel would have to be viewed apart from the law, grace apart from sin, faith apart from repentance, and Jesus apart from his humanness.

Adoptionism, 3rd century AD

Heretical belief: God adopted Jesus, a mere man, as his son because Jesus was sinless, thus making him a deity.

What the Bible says:

“In the beginning was the Word, and the Word was with God, and the Word was God.” (John 1:1; 3:16; see also 1 Tim 2:5)

Implication: If Jesus were a sinless man that God happened to “notice” after seeing his good deeds, then the prophecies about Jesus’ death and resurrection as the perfect, sinless lamb of God are senseless.

Sabellianism (also called “Modalism”), early 4th century AD

Heretical belief: Jesus and the Father are not three distinct persons but “modes” or “aspects” of a single being.

What the Bible says:

“But the Helper, the Holy Spirit, whom the Father will send in my name, he will teach you all things and bring to your remembrance all that I have said to you.” (John 14:26; see also Matt 3:17; 27:46; John 5:20; Heb 9:14)

Implication: If God is divisible, he can change—and that means the doctrine of the Trinity would have to be discarded.

Arianism, 4th century AD

Heretical belief: Jesus was a created being, and therefore, the divinity of God the Father must be distinguished from the divinity of Christ.17

What the Bible says:

“I and the Father are one.” (John 10:30; see also Exod 3:14; John 1:1; John 8:58–59)

Implication: If Jesus was created by the Father and is not the same substance as the Father, then he is a finite being and not part of the full Godhead.

Pelagianism, late 4th–early 5th century AD

Heretical belief: Adam’s sin did not affect future generations. People are not inherently sinful. They can avoid sin and choose to live righteous, holy lives according to God’s will and merit salvation by good works apart from his grace.18

What the Bible says:

“Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned . . . But the free gift is not like the trespass. For if many died through one man’s trespass, much more have the grace of God and the free gift by the grace of that one man Jesus Christ abounded for many. 16 And the free gift is not like the result of that one man’s sin. For the judgment following one trespass brought condemnation, but the free gift following many trespasses brought justification. For if, because of one man’s trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ.

Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. For as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous (Rom 5:12, 5:15–19; see also Ps 51:5)

Implication: If Christians have to work their way to God, there is no need for his free gift of salvation.

Why the topic of heresy matters

Today’s culture tends to affirm that what a person believes—especially regarding religion and faith—is their own prerogative. And in one sense, it is: God permits his image-bearers to rebel against him in countless ways before judgment day. However, in the prologue to his book Heresies and How to Avoid Them: Why It Matters What Christians Believe, Ben Quash says there is a good reason Christianity has been “so concerned about orthodoxy, or right belief”:19

The Church’s identity and integrity were expressed in orthodoxy: the confession (and enactment) of a collective belief. Christianity was open to anyone, but it had definite convictions. That’s why heresy was a matter to be taken seriously—because it called those convictions into question. It threatened a crucial thing that bound the Church together and made Christians Christians.20

This is why the topic of heresy matters for us today. Not everyone will dive deep into the history of heresy, but being aware of some of the false teachings that crept into the early Church—and still show up today—will strengthen a person’s understanding of correct doctrine. It will help to keep the body of Christ knitted together.

Learn how Logos can help you research more
about topics like heresy.

The creeds, “boundaries of faith”

The early Church protected itself against heretical teaching with summaries of Christian truth called, in Greek, “canons of truth” and, in Latin, the “Rule of Faith” (regula fidei). These eventually developed into formal creeds, or affirmations of the faith:21

Justin Holcomb, a theology professor at Reformed Theological Seminary and Gordon-Conwell Theological Seminary, calls the creeds “boundaries of faith that separate orthodoxy from heresy.” He writes:

Creeds and confessions are tools that the Church has used to speak about God clearly and faithfully, to guide its members closer to God, and sometimes to distinguish authentic Christianity from the innovations, heresies, and false teachings that the New Testament warns of.22

Each creed has a different purpose, but Holcomb says they all attempt “to communicate complex theological ideas to people who don’t have sophisticated theological backgrounds.”

Why we must guard against heresy

C. S. Lewis wrote of what he called “chronological snobbery”—assuming our modern-day values and beliefs are somehow automatically better than beliefs of the past. Yet we have just as much of a chance (if not more) to embrace false teaching as those early believers did. With the advancement of technology and social media, opportunities are plenty for false teaching to creep into the thoughts and hearts of well-meaning Christians. Without realizing it, if we’re not grounded in biblical truth, we might follow teachers and leaders who seem good and right but whose teaching is divisive or even erroneous.

God’s Word must be our plumbline—and as Paul exhorted, we must “test everything” and “hold fast what is good” (1 Thess 5:21).

There’s one more kind of heresy that often goes unnoticed, yet the concept surfaces throughout the New Testament. Some have called it a “lifestyle” heresy. This is when the believer’s life does not align with God’s instruction in the Bible and therefore does not point people to Jesus. Titus 2:1–10 lists what a life in Christ looks like—among a long list of characteristics, it’s one that is self-controlled, loving, and dignified.

But it’s verse 10 that answers why we should live this kind of life:

. . . so that in everything [we] may adorn the doctrine of God our Savior. (Emphasis added)

We must “adorn” (or in Greek kosmeō, meaning “to ornament” or “to make attractive”23) sound doctrine. Why? Verses 11–14 tell us:

For the grace of God has appeared, bringing salvation for all people, training us to renounce ungodliness and worldly passions, and to live self-controlled, upright, and godly lives in the present age, waiting for our blessed hope, the appearing of the glory of our great God and Savior Jesus Christ, who gave himself for us to redeem us from all lawlessness and to purify for himself a people for his own possession who are zealous for good works.

Jesus, our “blessed hope,” is coming back. But in the meantime, the world is not getting any prettier. Subtle, heretical teachings and Christians living “heretical” lives will distract people who don’t know the Savior from the pure gospel of Jesus Christ. Instead, our lives and what we teach should accurately reflect who Jesus is to a lost world that desperately needs him.

See how Logos can help you in your study of the Bible.

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  1. Daniel G. Reid et al., Dictionary of Christianity in America (Downers Grove, IL: InterVarsity Press, 1990).
  2. https://www.merriam-webster.com/dictionary/heresy
  3. Bird, “History of Heresies.”
  4. Bird, “History of Heresies.”
  5. Jeffrey E. Miller, “Heresy and Orthodoxy in the New Testament,” ed. John D. Barry et al., The Lexham Bible Dictionary (Bellingham, WA: Lexham Press, 2016).
  6. Bird, “History of Heresies.”
  7.  (Ant. xiii.5.9[171])
  8. Bird, History of Heresies.
  9. Beth Felker Jones, Christian Thought: Orthodoxy and Heresy, Logos Mobile Education (Bellingham, WA: Lexham Press, 2016).
  10. Jones, Christian Thought.
  11. Justin S. Holcomb, Know the Heretics, part of the Zondervan Know Series (Zondervan, 2019).
  12. Walter A. Elwell and Philip Wesley Comfort, Tyndale Bible Dictionary, “Judaizers,” Tyndale Reference Library (Wheaton, IL: Tyndale House Publishers, 2001), 752.
  13. Derek Brown, “Docetism,” ed. John D. Barry et al., The Lexham Bible Dictionary (Bellingham, WA: Lexham Press, 2016).
  14. Charles Taliaferro and Elsa J. Marty, eds., “Marcionism,” A Dictionary of Philosophy of Religion (New York; London; Oxford; New Delhi; Sydney: Bloomsbury Academic: An Imprint of Bloomsbury Publishing Inc; Bloomsbury, 2018), 174–175.
  15. Zachary G. Smith, “Gnosticism,” ed. John D. Barry et al., The Lexham Bible Dictionary (Bellingham, WA: Lexham Press, 2016).
  16. Charles Taliaferro and Elsa J. Marty, eds., “Marcionism,” A Dictionary of Philosophy of Religion (New York; London; Oxford; New Delhi; Sydney: Bloomsbury Academic: An Imprint of Bloomsbury Publishing Inc; Bloomsbury, 2018), 174–175.
  17. John D. Barry et al., eds., “Arianism,” The Lexham Bible Dictionary (Bellingham, WA: Lexham Press, 2016).
  18. John D. Barry et al., eds., “Pelagianism,” The Lexham Bible Dictionary (Bellingham, WA: Lexham Press, 2016).
  19. Ben Quash, “Prologue,” in Heresies and How to Avoid Them: Why It Matters What Christians Believe, ed. Ben Quash and Michael Ward (Grand Rapids, MI: Baker Academic: A Division of Baker Publishing Group, 2012), 1–2.
  20. Ben Quash, “Prologue,” in Heresies
  21. Brannon Ellis, Mark Ward, et al. Lexham Survey of Theology, “Rule of Faith,” (Lexham Press, Bellingham, WA) 2016.
  22. Justin Holcomb, “Why Study Heresies, Creeds, and Councils?Credo Magazine, 2020 November 20.
  23. Kosmeō comes from the word kosmos, where we get our English word “cosmetic,” what women use to beautify themselves. It’s the idea of putting something in proper order so it’s symmetrical, appealing.
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Written by
Karen Engle

Karen Engle is a copy editor for Faithlife. She has a master's in biblical studies and theology from Western Seminary and frequently takes groups to Israel.

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Written by Karen Engle