Martin Luther is a pivotal figure for any Protestant. His famous distinction between Law and Gospel arose from Augustine’s way of relating law and grace.¬†Luther embraced Augustine’s message in¬†On the Spirit and the Letter (De spiritu et littera) that the law of God can only terrify us if it comes to us without the grace of God. Just add that the Gospel of Christ is a means of grace, with a kind of sacramental efficacy to give the grace it signifies to those who believe, and you have the core of Luther’s Protestantism.