On January 3, 1521 the Vatican published the bull Decet Romanum Pontificem ([It] Befits [the] Roman Pontiff), excommunicating Martin Luther for Luther's refusal to recant. The pope had issued a previous bull, Exsurge Domine (Arise, O Lord), giving Luther 60 days to recant and another 60 days to make his recantation known to Rome. Meanwhile, Luther's books were being burned for allegedly containing heresy. On December 10, 1520 Luther responded by publicly burning his copy of Exsurge Domine.
The Church usually handed excommunicated persons over to civil authorities to be burned at the stake. However, circumstances prevailed that spared Martin Luther this fate and paved the way for Luther's stand at the Diet of Worms in April 1521. The pure teaching of Scripture would not be snuffed out by the flames.
Luther wasn't looking to split the Church; he wanted the Church to institute reforms and took a more conciliatory tone at first in his writings. When it became clear that the pope cared not at all for Scripture and reason, only for Luther's recantation, Luther rose to the challenge and prepared to take his stand. The truth of God's Word, long muffled or distorted by the noise of human traditions, would find a voice in Martin Luther and others willing to risk everything on the authority and benevolence of Sola Scriptura.
Roland H. Bainton, Here I Stand: A Life of Martin Luther (Plume, 1995)
[Republished in a very nice hardcover by Hendrickson Publishers in 2009: see here.]