On October 31, 1517, Martin Luther nailed his 95 Theses to the Wittenberg Castle Church door, challenging papal authority and the practice of selling indulgences. Luther is known for his emphasis on the authority of the Scriptures and his teaching of justification by faith in Christ alone. But Luther also made significant contributions to hymnody, being credited with 37 hymns and the restoration of congregational singing in the worship service. The chief function of music for Luther was the proclamation of the Word of God, and especially the clear Gospel message. Through his hymns, written in the language of the people rather than Latin, and through his translation of the Bible into German, the Gospel became accessible to the common people, and the Word and the Spirit brought about spiritual reformation.