It’s helpful, as with his Third Way, to begin with a metaphor, in order to get an intuitive feel for the proof.
Imagine that you are an astronomer on a world with one moon. It is always night on your world, and the moon is the only body in the sky.
Nature is like a stack of books, sessile, until moved.
In my ongoing debate with biologist Jerry Coyne, frequent reference is made to Aquinas’ Five Ways, particularly to his Prime Mover argument.
The greatest engine of atheism in modern times — Darwin’s theory — is nothing more than a bastardization of the strongest philosophical argument for God’s existence.