At the age of 15 he entered the Franciscan monastery at Avignon, and after 1517 he was an itinerant preacher, travelling through France, Italy and Switzerland.
Lambert's study of the Scriptures shook his faith in Roman Catholic theology, and by 1522 he had abandoned his order, and became known to the leaders of the Reformation in Switzerland and Germany.
He did not, however, identify himself either with Zwinglianism or Lutheranism; he debated with Huldrych Zwingli at Zürich in 1522, and then made his way to Eisenach and Wittenberg, where he married in 1523.
He was, however, befriended by Jacob Sturm, who recommended him to the Landgraf Philip of Hesse, the most liberal of the German reforming princes.
[1] Philip continued to favor Lambert, who was appointed professor and head of the theological faculty in the Landgraf's new University of Marburg.