Cur Deus Homo (Why God Became Man)

Anselm of Canterbury was a Benedictine monk and a philosopher who held the office of Archbishop of Canterbury from 1093 to 1109. Called the founder of scholasticism, he is famous as the originator of the ontological argument for the existence of God. Anselm was proclaimed a Doctor of the Church in 1720 by Pope Clement XI.
Although he believed, Anselm constantly struggled to make sense of his religion. He considered the doctrines of faith an invitation to question, to think, and to learn, and he devoted his life to confronting and understanding the most elusive aspects of Christianity. Monologium, his writings on matters such as free will, the nature of truth, and the existence of God, established Anselm one of the greatest theologians and philosophers in history.
In Why God Became Man, Anselm tries to answer the question of the incarnation of God in the form of Jesus Christ, concluding that neither men nor God owed anything to the Devil, and that man's only debt was to God.
Anselm was equally radical in his emphasis on human reason, and readers eventually notice that some of his writings were unusual because they don't contain references to the Scriptures.