I can't see or prove electricity exist,but it is there, I can't see air, but it's there, I can't see radio waves but my radio says it's there. There are many things we can't see,hear or even feel but we know they are there because we see or feel proof of it. God is spirit, we can't see or feel Him with our limited sences, but we can see proof all around us that He is there. Without faith no man can see or please God. We have to accept Him with the faith of a little child. If you need concrete proof of His existence, then you don't need faith. No man can look upon the face of God and live, even Moses could only see God's back. Jesus, who was God in the flesh, said "you have see me, you have seen the Father".