"For since the creation of the world God's invisible qualities--his eternal power and divine nature--have been clearly seen, being understood from what has been made, so that people are without excuse." Romans 1.30
With commendable sleight of hand, medieval philosopher Anselm of Canterbury came within a whisker of proving the existence of God. His clever theory that, because God must be greater than the greatest thing one could imagine, he must be real because being real is superior to being merely thought about, was undermined only by the absurdity of its implication for other propositions - eg the perfect pudding, the ideal home, &c.
Maybe it's just as well. It seems somehow demeaning that God should be "proved" by human ingenuity when, as the scripture says, he has provided ample proof of his own! At the end of the day, we see through faith and not sight. In other words our perception of God does not depend on own abilities but is a gift of faith.
So how does that square with the assertion that those who deny God are "without excuse"? Perhaps they simply haven't been fortunate enough to receive the gift? Either Paul is referring to Christians who deny God, despite their ability to perceive him or that gift has, in fact, been universally distributed but not everybody realises. But now we are straying into the murky waters of God's sovereignty and his right to choose whom he will save.
Or could it be that God has provided both the proof and the gift and will grant awareness according to his justice and mercy? We shall drive ourselves mad trying to second guess God. Better to receive gratefully what he chooses to reveal and pray for grace and understanding according to our capacity to receive and share them. Let God be God and let us concentrate on being his faithful witnesses and followers...