First Reading at today's Mass was from Isaiah. I started thinking about how amazing it was that the Old Testament prophets and the psalmists consistently believed in one God and spoke and prayed to him with such intimacy ~ God must have communicated with them. Then Jesus showed up and fulfilled all their prophecies, so Jesus must have been sent by God.
I am just applying my common sense, not trying to prove that the one God exists. First of all, admitting that I am a creature by God, I am already acknowledging his existence. Besides, I know that a lesser being is in no position to prove anything about a greater being. Just wanting to seek such proofs is being arrogant and would render faith meaningless. God is to be believed in and trusted! Any other way will not gain me entrance.