But the cornerstone of religion -- all religions, as far as I know -- is Faith. "Belief in things unseen," to be sure, but also an admission that there are things unknown and unknowable, but that exist nonetheless. In Buddhism, that's Zen: where does a circle begin? What is the sound of one hand clapping? How long is a piece of string? If a tree falls in the forest ...
In Christianity, it is a belief -- not a PROOF -- in God the Father, God the Son, and God, the Holy Spirit. Unanswerable, unknowable, but certain.