Every Christian who has met Jesus in a real and personal way knows without a moments hesitation that God is absolutely, positively real.
". . . But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned" (1Co 2:14 AV).
He was not a spiritual man, nor are any of those who merely believe in "intelligent (intellectual) design" which is also yet another invention of a "natural" mind, a process incapable of conveying the deep things of the Spirit of God to the human heart.