Saint Thomas Aquinas

Saint Thomas Aquinas (1225-1274), of Italy, was the greatest Christian theologian and philosopher. In his Summa Theologica he used Aristotelian logic to clarify and support the tenets of the Christian faith and thereby laid the basis of Roman Catholic theology. He attempted. with more success than any other thinker, to reconcile faith and reason and give Christianity a firm intellectual foundation.

So, whatever is moved must be moved by something else. If that which moves it is itself moved, then it too must have been moved by something else, and that by something else again. But this process cannot go on to infinity, for then there would be no first mover, and therefore no other mover since the subsequent movers can move only insofar as they are moved by the first mover, as the cane moves only insofar as it is moved by the hand. So it is necessary that there be a first mover, which is moved by nothing else; and this we all understand to be God.

St. Thomas Aquinas, Summa Theologica (1256-1272. Paraphrase of translation by the English Dominican Fathers, 1912- 1936, in Introduction to St. Thomas Aquinas, A.C. Pegis, ed., 1948)