The Pope claimed to inherit the keys of St Peter, which opened the treasury containing the good works of the saints and the boundless merits of Jesus Christ. He professed to be able to transfer a portion of this merit to any person who gave a sum of money to purchase pardon for sins. "Indulgences" had been first granted to pilgrims and Crusaders. They were further extended to those who aided pious works, such as the building of St Peter's. The Pope, Leo X, had found the papal treasury exhausted by his predecessors. He had to raise money, and therefore allowed agents to sell pardons throughout Germany. Tetzel, a Dominican friar, was employed in Saxony. He was noisy and dishonest, and spent on his own evil pleasures sums that were given by the ignorant creatures upon whom he traded to secure their eternal happiness.

Luther inveighed against such practices from the pulpit of the church at Wittenberg. He was particularly angry to hear Tetzel's wicked proclamation that "when one dropped a penny into the box for a soul in purgatory, so soon as the money chinked in the chest, the soul flew up to heaven."

The papal red cross hung above Tetzel's money-counter, and he sat there and called on all to buy. Luther decided on an action that should stop the shameful traffic, declaring, "God willing, I will beat a hole in his drum." On the eve of All Saints' Day a crowd assembled to gaze at the relics displayed at the Castle church of Wittenberg. Their attention was drawn to a paper nailed on the church gate, which set forth reasons why indulgences were harmful and should be immediately discontinued.

There were other abuses in the Church of Rome which Luther now openly deplored. Hot discussion followed this bold step. Tetzel retired to Frankfort, but from there he wrote to contradict the new teaching of the Augustine monk. He burnt Luther's theses publicly, and then heard that his own had been consigned to the flames in the market-place of Wittenberg, where a host of sympathisers had watched the bonfire with satisfaction. Luther did not stand alone in his struggle to free the Church from vice and superstition. He lived in an age when men had learning enough to despise the trickery of worldly monks. The spirit of inquiry had lived through the Revival of Letters and Erasmus, the famous scholar, had discovered many errors in the Roman Church.

Erasmus joined Luther in an attempt to show men that the Holy Scriptures alone would offer guidance in spiritual matters. He knew that a reform of the Western Church was urgently needed, and was willing to use his subtle brains to confute the arguments of ignorant opponents. But soon he found that Luther's temper was too ardent, that there was no middle course for this impetuous spirit. He dreaded for himself the loss of wealth and honour, and refused to make war on those in high stations, whose patronage had helped him to the rewards of knowledge.

Alarmed by the spread of Luther's books and doctrines, the cardinals entreated the Pope to summon him to Rome. Printing had been invented, and poor as well as rich could easily be roused to inquire into the truth of the doctrines taught by Rome. Leo X had been disposed to ignore the sermons of the obscure German monk, for he had many schemes to further his own ambition. He yielded, at last, and sent the necessary summons. Luther was loth to go to Rome, where he was sure of condemnation. The Elector Frederick of Saxony came forward as his champion, not from religious motives, but because he was pleased to see some prospect of the exactions of the court of Rome being diminished.

Cajetan, the Papal Legate, came to preside over a Diet, summoned specially to Augsburg. He urged the monk to retract his dangerous doctrine that the authority of the Bible was above that of the Pope of Rome. "Retract, my son, retract," he urged; "it is hard for thee to kick against the pricks." But the conference ended where it had begun—Luther fled back to Wittenberg.

He began to see now that the whole system of Romish government was wrong, and that there were countless abuses to be swept away before the Church could truly claim to point the way to Christianity. Conscience or authority, the Scriptures or the Church, Germany or Rome? A choice had to be made, each man ranging himself on one side or the other. The independence of Germany was dear to Luther's heart. He wrote an address to the nobles and summoned the Christian princes of Germany to his aid. He declared that all Christians were priests, and that the Church and nation ought to be freed from the interference of the Papacy. He was becoming an avowed enemy of the Pope, losing his former reluctance to attack authority. A Bull was, of course, issued against him, but the students of Erfurt threw the paper on which it was written into the river, saying contemptuously—"It is a bubble, let it swim!"

In December, 1520, Luther himself burnt the Bull on a fire kindled for the purpose at the Elster Gate of Wittenberg. He said, as he committed the document to the flames, "As thou hast vexed the saints of God, so mayest thou be consumed in eternal fire." The act cut him off from the Papacy for ever. He had defied the Pope in the presence of many witnesses. Charles V, the Holy Roman Emperor, was not in a position to take up the cause of Luther against his powerful enemies. He maintained an alliance with the Pope so that he would oppose the vast schemes which his rival, Francis I of France, was maturing. At the same time, he owed a debt of gratitude to the Elector Frederick, who was one of the seven German princes possessing the right to "elect" a new emperor. He decided, after a brief struggle, to yield to the demands of the Papal Legates. He ordered Martin Luther to come to Worms and appear before the great Diet, or Assembly of German rulers, which met in 1521.

Luther obeyed at once, making a triumphant journey through many towns and villages. Music fell on his ears pleasantly, a portrait of Savonarola was sent to him that he might feel his courage strengthened. Had not his resolve been fixed, he would have turned back at Weimar, where he found an edict posted on the walls ordering all his writings to be burnt. "I am lawfully called to appear in that city," he said, "and thither will I go in the name of the Lord, though as many devils as there are tiles on the houses were there combined against me." He was stricken with illness at Eisenach, but went on as soon as he recovered. When he caught sight of the old towers of Worms, his spirit leapt with joy, and he began to sing his famous hymn, "Ein feste Burg ist unser Gott." ("A mighty fortress is our God.")