Since all of St. Thomas’s proofs for God’s existence speak of a finite causal sequence leading to the divine, then why not just take any causal sequence back a few steps until one hits God? It should be simple enough to do this, right?
In fact, it is. It is never too hard to analyze an action back till we see it proceeding from some nature, the next step back hits the divine. The trick is to see why nature is simply a way of being open to divine activity. St. Thomas argues that nature is a source of action that moves others only by being itself moved; causes only by itself being caused; is from another, even when it’s necessary; is finite though it manifests the reality of what is not finite; is directed by another.
Once one sees what nature means in the five ways, the conclusion to the supernatural and divine is immediate.