In 1505 Luther entered a monastery under the delusion, common at that time, that the best service to God was to abandon home, family, and the world for which Christ died. His friends and especially his father were dismayed:

Was it for this that the father had pinched and saved, and denied himself and his [family] all manner of small comforts, that his boy should become...a monk, to add one to the overflowing crowd of “rogues and hypocrites,” as the sturdy old peasant called them?
...Many an old student friend, and some of his former professors, watched the black-robed figure slowly disappear behind the convent door, and went home to curse the monks who had robbed the university of its most distinguished student.… [7]

Luther soon picked up the ascetic practices of the monks, at least once spending three days without eating or drinking. At one point he was missed from the services and was discovered unconscious on the floor of his cell.

In his frustration and perplexity, Luther was driven to the Bible.

Luther later said, “If ever a monk could win heaven by monkery, I must have reached it.” [8] Yet for all the severe treatment of his body, he gained no sense of pardon nor of an inward welling up of spiritual life. In his frustration and perplexity, Luther was driven to the Bible. He studied the Epistle to the Romans again and again in hope of discovering the way to be right with God. The following account is his own:

I sought day and night to make out the meaning of Paul; and at last I came to apprehend it thus: Through the gospel is revealed the righteousness which availeth with God—a righteousness by which God, in His mercy and compassion, justifieth us; as it is written, “The just shall live by faith.” Straightway I felt as if I were born anew. It was as if I had found the door of Paradise thrown wide open. Now I saw the Scriptures altogether in a new light—I ran through their whole contents as far as my memory would serve, and compared them, and found that this righteousness was really that by which God makes us righteous, because everything else in Scripture agreed thereunto so well. The expression, “the righteousness of God,” which I so much hated before, now became dear and precious—my darling and comforting word. [9]

Thus Luther found the peace he had sought simply by taking God at His Word and trusting in His promises.

Luther was ordained a priest two years after entering the monastery. It became his duty to perform the sacrifice of the mass.

He thought it was now in his power to bring the Lord Jesus Christ down from heaven to earth, to change bread and wine into “the actual body of Christ which had hung on the Cross,

“The just shall live by faith.”...It was as if I had found the door of Paradise thrown wide open.

and the actual blood which had gushed forth at the thrust of the Roman soldier's spear.” [10] At this point Luther was also prescribing penances for those who sinned, for the Latin Bible, the Vulgate, did not command men to repent but to do penance. Years afterward, Luther's friend Melanchthon showed him that the Greek word actually means “change your mind” and does not refer to penance.