In his academical lectures Luther still remained faithful to that path which he had struck out on entering the theological faculty. He wished simply to propound the revealed word of God, by explaining the books of the Old and New Testaments; though he took pains in these lectures, in which he devoted several terms to the study of a single book, to explain thoroughly and impressively the most important doctrines of Christian faith and conduct. Thus he occupied himself during the time of the contest about indulgences, and after the autumn of 1516, with the Epistle to the Galatians, wherein he found comprised clearly and briefly the fundamental truth of salvation, the doctrine of the way of faith, of God's laws of requirements and punishments, and of gospel grace. He then turned anew to the Psalms, dissatisfied with his own earlier exposition of them. His exposition of St. Paul's Epistle he had sent to the press whilst engaged in his preparations for the Leipzig disputation. His opponents, he says here, might busy themselves with their much larger affairs, with their indulgences, their Papal bulls, and the power of the Church, and so on; he would retire to smaller matters, to the Holy Scriptures and to the Apostle, who called himself not a prince of Apostles, but the least of the Apostles. He also now began the printing of his work on the Psalms. Crowds of listeners gathered around him; his audience at times numbered upwards of four hundred. During the three years following the outbreak of the quarrel about indulgences, the number of those who matriculated annually at the university increased threefold. Luther wrote to Spalatin that the number of students increased mightily, like an overflowing river; the town could no longer contain them, many had to leave again for want of dwellings.