In the fall of 1252, Thomas Aquinas went to Paris to study theology. After 4 four years Aquinas received permission to teach theology at the university. He lectured on the Sententiae (Sentences) of Peter Lombard and the Gospel of Matthew. In the spring of 1256, Aquinas was incepted as a master of theology, and was regent master in theology at Paris until 1259. During that time he began writing one of his major works, the Summa contra Gentiles (Summary against the Gentiles).

The Summa contra Gentiles shows Aquinas putting forward important arguments in favor of the Christian faith. This Summary was for the benefit of missionaries working among Jews and Muslims. Aquinas left Paris for Naples in 1259, where he was head of the Dominican house of studies.

The Summa contra Gentiles is a profoundly significant work in the history of philosophy. In many ways it acts as an encyclopedia of the learning of the day in that we can find our way into the mental life of the era in which it was written. Keep in mind that this work contains the lectures of a great Doctor at the most prestigious university in Europe in the middle of the thirteenth century. Aquinas divides the Summa contra Gentiles into four books. The first three books try to set out theological positions that can be established by philosophical reasoning alone. Book IV, an exposition of scripturally revealed doctrine, complements the first three books. The topics of these books are as follows:

Book I: Of God as He is in Himself—This deals with the method of discussing God, whether God’s existence can be proved, God’s nature and other attributes.

Book II: God the Origin of Creatures—Book II examines God as creator and the nature of creation, while paying particular attention to the nature of human beings.

Book III: God the End of Creatures—This book considers God as the good and the end (goal) of purposive action and his providential government, especially regarding rational creatures.

Book IV: Of God in His Revelation—Book IV deals with Christian teaching on the trinity and incarnation, the sacraments, the resurrection of the dead and their final state.