The Reformation is a 16th-century movement in Western Europe when many leaders of the Catholic Church mounted efforts to rid the church of what they perceived to be corruption and false teachings. These leaders understood themselves to be recapturing the biblical faith and/or the best of the ancient traditions of the faith. (In the case of Martin Luther this meant a return to Paul’s teaching of justification by grace through faith.) When Catholic leaders failed to move quickly enough or thoroughly enough on the reforms demanded, various Protestant bodies, including Lutheranism, emerged.
Ellingsen, Mark, "Who, What, When, Where, and Why: Reformation Basics" (2016). Interdenominational Theological Center Faculty Publications. 8.
In Ever-Reforming: A Reformation 500 Cross-generational Study, edited by Mindy Makant and Eric Childers, 17-18. Salisbury, NC: North Carolina Synod, 2016