Luther pointed out [in the controversy over indulgences] that by working with Erasmus's edition of the Greek New Testament, he had discovered that Staupitz [the vicar general of the Augustinians for Germany and Luther's friend] had been right [in his emphasis of "the inclination of the heart rather than particular sins or particular good works as a determinant of the status of the soul"]and that common confessional practices had no basis in the Scriptures. The Latin translation of Jesus' command at Matthew 4:17 read, "Do penance, for the kingdom of God is at hand." But the Greek said, "Be penitent. . . '" Therefore God demanded not outward deeds but a changed heart and mind. "Doing" had literally nothing to do with salvation, particularly with regard to indulgences. "To repent" and "to do penance" were two different things.
-from Kittelson, Luther the Reformer: the Story of the Man and His Career. (Fortress Press edition 2003) at p. 113.
The Douay-Rhems 1899 American Edition continued to translate, "Do penance, for the kingdom of heaven is at hand."
The New Revised Standard Version, Anglicised Catholic Edition (NRSVACE), however, translates, "Repent, for the kingdom of God is at hand."
Kittleson's 1986 biography is a worthy successor to Bainton's, Here I Stand, a Life of Martin Luther, a 1950 work, but I would never, ever forgo the opportunity to read Bainton.