Get a well-rounded bundle of Reformation theology, history, and ideology in the T&T Clark Lutheran Reformation Day Collection. You’ll see traditional as well as cutting-edge analyses of Lutheran theological positions, this Lutheran movement in church history, and the influence of Lutheran thinkers on recent theology. This readable yet scholarly collection is a perfect entry point or add-on to any modern Protestant library.
Make sure to check out the exhaustive Lutheran systematic theology, Theological Commonplaces by Johann Gerhard (6 vols.).