God reveals Himself to all of humanity by the things created, humans are the only creatures able to work this out by virtue of been rational, so the only creatures that can claim ignorance are irrational creature, human are without excuses. But it seems that unless God gives a human the capacity to believe and hope for thing not seem, that is to say give them the gift of faith it is impossible for some to believe, I am partial to the doctrine that we are reprobates till God in His mercy gives us the gift of faith, there are no responses so far in this thread that say that people believe in God by any other means but by faith. In Christianity we have:
Luk 22:31 And the Lord said, Simon, Simon, behold, Satan has desired you, that he may sift you as wheat.
Luk 22:32 But I have prayed for you, that your faith fail not. And when you are converted, strengthen your brothers.
Act 26:18 in order to open their eyes so that they may turn from darkness to light, and from the authority of Satan to God, so that they may receive remission of sins and an inheritance among those who are sanctified by faith in Me.
Rom 1:17 For in it the righteousness of God is revealed from faith to faith, as it is written, "The just shall live by faith."
Rom 5:2 Through Him we also have access by faith into this grace in which we stand, and we rejoice on the hope of the glory of God
1Co 12:8 For through the Spirit is given to one a word of wisdom; and to another a word of knowledge, according to the same Spirit;
1Co 12:9 and to another faith by the same Spirit; and to another the gifts of healing by the same Spirit;
This is just about all I needed to believe that God exist.