The universe and our existence are contingent. This we know. We know that the universe didn’t always exist and will eventually suffer a heat death. This means that the existence of the universe is contingent on other factors and is not a brute fact in and of itself. It is not possible that the universe pulled itself up by it’s own bootstraps. Even if the universe is the latest in a string of universes or is part of a multiverse (implying that the universe was caused by other, non-divine entities), all that has been done is to multiply the number of contingent entities. There still must be something logically necessary behind it all. This logical necessity is God; the maximally greatest being possible.