Oswald Bayer, Martin Luther’s Theology, p. 268:

A Christian believer never develops beyond baptism, as long as he or she lives, no matter how much one has grown, no matter how much one has learned, and no matter what changes one has experienced. For in baptism one already has everything that comes with the name of God. That ship is unsinkable.

In short, the “Christian life is nothing else than a daily baptism” (Sanctification by the gospel).