There are a number of reasons why Paul wrote this letter. First, there was the matter of Epaphroditus and the gift sent to Paul by his hand. Paul wished to respond to their generosity. Second, he took the opportunity to share certain news about himself and his situation. Third, he wished to address a serious problem of division within the church. Fourth, Paul wished to warn about those he calls "dogs," "men who do evil," and "mutilators of the flesh" in 3:2. In addition to these central purposes there are certain themes sounded throughout the book which can be an enriching pursuit by the serious student.
“Following Christ was a relationship in which divine realities existed, not just a rule-keeping religion” (Philippians 2:1)
“His intent was not to produce anxiety, but to promote seriousness and maximum dedication to the task.” (Philippians 2:12)
“‘Thanksgiving’ (εὐχαριστία, eucharistia) recognized God’s blessings and control of circumstances. Anxiety tends to forget God, to rely on human resources. So both prayer and a recognition of God’s love and goodness are powerful, and together they are most effective. Recall God is the God who urges men to pray (Luke 11:9–13). Will their self-centeredness turn them away from real help?” (Philippians 4:6)
“But Paul’s view of reconciliation was broader than peace between man and God. It sweeps through earth and heaven and encompasses all of reality.” (Colossians 1:20)
“Anxiety can produce irritability and defensiveness. It is a soil in which discord could grow.” (Philippians 4:6)