Another proof of the existence of God, this time by Thomas Aquinas:
[link to www.fordham.edu
"The first and plainest is the method that proceeds from the point of view of motion. It is certain and in accord with experience, that things on earth undergo change. Now, everything that is moved is moved by something; nothing, indeed, is changed, except it is changed to something which it is in potentiality. Moreover, anything moves in accordance with something actually existing; change itself, is nothing else than to bring forth something from potentiality into actuality. Now, nothing can be brought from potentiality to actual existence except through something actually existing: thus heat in action, as fire, makes fire-wood, which is hot in potentiality, to be hot actually, and through this process, changes itself. The same thing cannot at the same time be actually and potentially the same thing, but only in regard to different things. What is actually hot cannot be at the same time potentially hot, but it is possible for it at the same time to be potentially cold. It is impossible, then, that anything should be both mover and the thing moved, in regard to the same thing and in the same way, or that it should move itself. Everything, therefore, is moved by something else. If, then, that by which it is moved, is also moved, this must be moved by something still different, and this, again, by something else. But this process cannot go on to infinity because there would not be any first mover, nor, because of this fact, anything else in motion, as the succeeding things would not move except because of what is moved by the first mover, just as a stick is not moved except through what is moved from the hand. Therefore it is necessary to go back to some first mover, which is itself moved by nothing---and this all men know as God. "