In addition to the famous 5 Ways, St. Thomas Aquinas provides another distinctly different argument for the existence of God found in the first part of the second part questions 1-5 of the Summa Theologica. It can be summarized as follows:
1. Human beings seek lasting happiness and complete fulfillment that cannot be attained through any finite or created thing.
2. Only something boundless, eternal, and uncreated could satisfy the deepest longings of the human soul.
3. God is by definition the uncreated good and the only Being capable of being man’s ultimate end.
4. A creature would not exist with a potency that can only be fulfilled by God if God did not exist.
5. Therefore, God exists.
The proof of this argument is that anyone who finds God on a personal level finds that which fulfills in a way that no finite created thing can. Only then is the heart at rest as St. Augustine most famously said.