What one is most convinced of is his or her own existence. Despite this, in purely scientific terms, everyone is a mystery. For man is not what he physically appears to be, but consists of what he calls I, and the I is not observable.

That is why when the philosopher Rene Descartes (1596-1650) wanted to give proof of his own existence, he did not say: “I consist of a body that is observable, therefore I exist.” Instead he had to say: “I think, therefore I exist.”

Man undoubtedly has an observable existence. We all know that man exists. But, in fact, this man’s existence is at the level of “I” and the cognizance of I is at the level of perception or comprehension, and not at the level of observation.

Exactly the same is true of God. It is, as if, God is a Greater I. God, at the level of His creation, is directly observable. But God at the level of His Being is not directly observable by man. We shall have to believe in God on the basis of the same logical principle which Descartes employed to know himself, and on which all men and women believe in their own existence.

I can comprehend God; therefore God exists. The truth is that God’s being comprehensible is an undeniable proof of His existence. If we deny God, we shall have to deny our own selves. Since we cannot countenance our own denial, we cannot countenance God’s denial either. Everyone who believes in his own existence is logically compelled to say, “I exist; therefore, God exists.”

Source: In Search of God