Sebastian Bach's organ music contained a mystic sense of the eternal. Widor, deeply impressed, agreed to teach Schweitzer without fee, and a great and influential friendship thus began. From 1893 Schweitzer studied Protestant theology at the Kaiser Wilhelm University in Strasbourg. There he also received instruction in piano and counterpoint from professor Gustav Jacobsthal, and associated closely with Ernest Munch, the brother of his former teacher, organist of St William church, who was also a passionate admirer of J. S. Bach's music. Schweitzer served his one-year compulsory military service in 1894. Schweitzer saw many operas of Richard Wagner in Strasbourg (under Otto Lohse) and in 1896 he managed to afford a visit to the Bayreuth Festival to see Wagner's Der Ring des Nibelungen and Parsifal, both of which impressed him. In 1898, he returned to Paris to write a PhD dissertation on The Religious Philosophy of Kant at the Sorbonne, and to study in earnest with Widor. Here he often met with the elderly Aristide Cavaillé-Coll. He also studied piano at that time with Marie Jaëll. In 1899, Schweitzer spent the summer semester at the University of Berlin and eventually obtained his theology degree at the University of Strasbourg. He published his PhD thesis at the University of Tübingen in 1899. In 1905, Schweitzer began his study of medicine at the University of Strasbourg, culminating in the degree of M.D. in 1913. Music Schweitzer rapidly gained prominence as a musical scholar and organist, dedicated also to the rescue, restoration and study of historic pipe organs. With theological insight, he interpreted the use of pictorial and symbolical representation in J. S. Bach's religious music. In 1899, he astonished Widor by explaining figures and motifs in Bach's Chorale Preludes as painter-like tonal and rhythmic imagery illustrating themes from the words of the hymns on which they were based. They were works of devotional contemplation in which the musical design corresponded to literary ideas, conceived visually. Widor had not grown up with knowledge of the old Lutheran hymns. The exposition of these ideas, encouraged by Widor and Munch, became Schweitzer's last task, and appeared in the masterly study J. S. Bach: Le Musicien-Poète, written in French and published in 1905. There was great demand for a German edition, but, instead of translating it, he decided to rewrite it. The result was two volumes (J. S. Bach), which were published in 1908 and translated