"For by grace are ye saved through faith," the Apostle Paul wrote to the Ephesians, "and that not of yourselves: it is the gift of God: not of works, lest any man should boast." This and related Pauline assertions were central to the 16th-century Reformation, and they remain integral to the self-understanding of Protestants around the world. That self-understanding has been challenged over the past three or four decades, owing to a dispute over a single word: "works."
The Protestant Reformers applied Paul's denunciations of works-based righteousness directly to late-medieval Catholicism's use of other good works to merit salvation: indulgences, prayers, sacraments, pilgrimages. The Protestants insisted that salvation is entirely a gift of God, received by faith. Even faith is part of the gift. Good works are the proper response to that gift but contribute nothing to its attainment. This served as the Protestant doctrine of "justification" for half a millennium.