Mysticism is an important stream of thought in the history of Christianity, and a parallel exercise of scholastic philosophy and theology in the Middle Ages. Bonaventure, a master of mysticism in the Middle Ages, is regarded as the peak and the soul of mysticism in the thirteenth century. His form of mysticism has a close relation to various schools of mysticism in the Middle Ages, such as the schools of Dionysius, St. Bernard, St. Victor, etc. Itinerarium mentis in Deum is Bonaventure's most famous works on mysticism in which he described six steps human mind ascending to God. Furthermore, Bonaventure's division of similitude between God and the world made a clear distinction between his theory and pantheism.