He didn’t get a chance to surf the web, or watch cat videos. So what did he do?
From May 4, 1521, to March 1, 1522, Luther remained at the Wartburg. There is little of his love of nature in the letters he wrote in solitude. He confides in Melanchthon, asking the question, “Who knows, in the counsels of silence, what work God is planning on these heights?”
He who is to receive a message from God, must be alone with the Alone. … All men who have a message to their fellows come to realize the justice of the remark Dr. Copleston addressed to Newman, once meeting him taking his lonely walk, “Nunquam minus solus quam cum solus.”
As Luther was about to leave the Wartburg in 1522 he assured his Elector that he “had received the Gospel not from man, but from heaven alone, through our Lord Jesus Christ.” That very year in his Wyder den falsch genantten geystlichen Standt he declared his word, office, and work to be from God. He was quite certain that Christ, who was the master of his doctrine, called him to be an evangelist and regarded him as such. Under pain of eternal wrath he was forced to preach the message which God had given him in a vision. In 1523 he was certain that he had his doctrines from heaven.
In the Wartburg his pen was not idle. He composed the booklet Von der Beicht ob der Bapst Macht habe zu gepieten, 1521, in which he thrusts aside the compulsory duty of confession. Man “is at liberty to make use of confession if, as, and where he chooses. If he does not wish you may not compel him, for no one has a right to or ought to force any man against his will. Nevertheless, absolution is a great gift from God. In the same way no man can or ought to be forced to believe, but every one should be instructed in the gospel and admonished to believe, though he is left free to obey or not to obey.
All the sacraments should be left optional to every one. Whoever does not wish to be baptized, let him be. Whoever does not wish to receive the sacrament has a right not to receive. Therefore, whoever does not wish to confess is free before God not to do so.” It is evident that he objects to constraint in the case of any of the sacraments. This dread of force is also clear in his letter to Haupold: “I will have no forcing and compelling. Faith and baptism I commend. No one, however, may be forced to accept it, but only admonished and then left free to choose.”*
Unfortunately his tolerant attitude vanished as soon as he returned to Wittenberg and the lunacy of Carlstadt.
*R.H. Murray, Erasmus & Luther: Their Attitude to Toleration (168–170).