In the year in which he had completed his terms in the Faculty of Law he found a post of organist at Halle: and in a church more than strictly Lutheran, being of the Reformed order, where the organist had expressly to conform to the new cult. However, he was only seventeen years old.[29] This simple fact showed what musical authority he already exercised in the town where he had studied law.[30] Not only was he organist, but he was also Professor at the College of the Reformists; he took vocal music there for two hours every week; he selected the most gifted of his pupils and formed from them a vocal and instrumental body which was to be heard every Sunday in one church or another of the town. He included in his musical repertoire, chorales, Psalms, motets, cantatas--which were changed every Sunday. Truly an excellent school for learning to write quickly and well. Handel there formed his creative fecundity.[31] Of hundreds of cantatas which he then wrote, none were preserved by him.[32] But it is certain that his memory retained more than one idea to serve in later compositions, for he never lost anything, and from that time for the rest of his life he retained in his mind his earlier musical ideas. This should not be attributed to his speed in working, but to the unity of his thought and his strenuous search for perfection. Handel renewed neither his yearly engagement at the Cathedral of Halle nor at the University. In his period as organist he had gauged his own musical force and he no longer wished to constrain it. A wider field of activity was necessary. He quitted Halle in the spring of 1703, and guided both by his instincts and by a preference of his master Zachau[33] he betook himself to Hamburg, the city of German Opera.