Therefore St. Peter says in 1 Peter 2:21 that Christ suffered for us (this insofar as it is a sacrament), “leaving you an example.” The sacrament of Christ’s Passion is His death and the remission of sins. The example, on the other hand, is the imitation of His punishments. Therefore he who wants to imitate Christ insofar as He is an example must first believe with a firm faith that Christ suffered and died for him insofar as this was a sacrament. Consequently, those who contrive to blot out sins first by means of works and labors of penance err greatly, since they begin with the example, when they should begin with the sacrament. Therefore the Gospel is neglected through unbelief of the heart, but the Law is neglected through the disobedience of the works.
Luther, Martin Luther’s Works: Volume 29: Lectures on Titus, Philemon, and Hebrews 123-124