THERE MUST BE A GOD because (a) since the beginning of history, the most variegated majority of people have intermittently believed there was; (b) it is hard to consider the vast and complex structure of the universe in general and of the human mind in particular without considering the possibility that they issued from some ultimate source, itself vast, complex, and somehow mindful; (c) built into the very being of even the most primitive human there seems to be a profound psychophysical need or hunger for something like truth, goodness, love, and—under one alias or another—for God; and (d) every age and culture has produced mystics who have experienced a Reality beyond reality and have come back using different words and images but obviously and without collusion describing with awed adoration the same Indescribability.
Statements of this sort and others like them have been advanced for several thousand years as proofs of the existence of God. A twelve-year-old child can see that no one of them is watertight. And even all of them taken together won't convince any of us unless our predisposition to be convinced outweighs our predisposition not to be.
It is as impossible to prove or disprove that God exists beyond the various and conflicting ideas people have dreamed up about God as it is to prove or disprove that goodness exists beyond the various and conflicting ideas people have dreamed up about what is good.
It is as impossible for us to demonstrate the existence of God as it would be for even Sherlock Holmes to demonstrate the existence of Arthur Conan Doyle.
All-wise. All-powerful. All-loving. All-knowing. We bore to death both God and ourselves with our chatter. God cannot be expressed, only experienced.