I know that, Gilbert. That is why I put the word ‘knows’ in quotation marks. A religious person does not know that God exists, but he claims to know that God exists.
Look at out friend, eanassir. He ‘knows’ that God of Islam is the true God, and that the punishments meted out by countries like Iran and Saudi Arabia (cutting hands of a thief, stoning a woman to death for adultery, killing of homosexuals, honour killings etc.) are prescribed by Allah.
A religious extremist is so sure of his faith, that he ‘knows’ his God is the true God, anybody who disagrees with him is a Disciple of the Devil and is headed straight for Hell.
An Atheist or an Agnostic on the other hand, cannot be sure. As an Atheist I think God doesn’t exist, but I cannot say that with 100% certainty. As I said before, how can anybody know that? However, a religious person ‘knows’ with 100% certainty that his God is the true God.