The true believer does not claim to know God. Religion is a system of faith. Faith is trust in what is unknown and unseen. Without trust, any association, bank, institution, or state is unworkable. Neither is science possible without it: faith in hypothesis.
Because the belief system is based on admission of ignorance, anyone who arrogates complete knowledge of God is either delusional or lying.
“What yesterday was still religion, is no longer such today; and what today is atheism, tomorrow will be religion.” -Ludwig Feurerbach : quoted by Chris Hedges in his book “America’s New Fundamentalists – When atheism becomes religion.”
“The only true wisdom is in knowing you know nothing.” – Socrates