In his book “Summa Contra Gentiles,” Thomas Aquinas made the connection between faith and reason, and heavily cites Aristotle as his logical influence. Aquinas did not put forth arguments like “the universe couldn’t have been started unless there was a God.” Instead, he referenced the Aristotelian idea that no potential can actualize itself unless it is created by something. Aquinas used an analogy for God the Father working through Jesus Christ, such as if you hit something with a stick, the stick is being struck against the object, but the stick couldn’t have done it without your hand. 

Thomas Aquinas confirmed two vital things: God exists, and He is pure. Because of these truths, Aquinas derived the following divine attributes: first, monotheism follows from God as a pure act; second, God is immaterial, since He cannot be changed; third, He is all-powerful, and causes everything that happens on earth; fourth, humans have intellect and will, and were made in the image of God, so He must also have those qualities; fifth, God is a good God, and has no negative features. 

Aquinas followed in the footsteps of Augustine of Hippo, who he claimed was one of the most significant early Christian scholars. Although he believed that war is inherently evil and can only be justified by the aggressor, Aquinas stated that there are some circumstances under which a war should be waged. 

Fransico de Victoria (1483-1546) proclaimed that princes should seek to live in peace, However if there is a war, it should be waged within just limits and followed by a period of moderation if possible. 

The Church eventually put restrictions on war, such as prohibiting crimes like robbing churches or peasants, leaving women and children alone, and not burning civilian homes. Christians also agreed to stop fighting on feast days.

John Duns Scotus (1265-1308) was an Scottish franciscan who taught theology at Oxford University. Scotus asserted that the existence of God, the immorality of the soul, and the providence of God are all truths, although none are  knowable by reason. However, it is by faith that one believes, he said. Scotus emphasised on the divine will and stated that whatever God wills is always good. 

William of Ockham, a colleague of Scotus, claimed that things do not have essences or natures and that reason and faith are separate. He stressed God’s will, stating that God could save the guilty and damn the righteous if He willed it. Interestingly, both of these scholars opposed Thomas Aquinas, who thought that reason and faith worked together in unison.