In the book, The Concept of God, Maulana Wahiduddin Khan explains that both revealed and scientific knowledge equally prove that there is a God of this universe. And that God is only one. Not believing in God is as illogical as believing in many gods. In this present world man is given freedom for the purpose of being tested. Everyone is free to say what he wants to and to believe in anything of his own free will. But so far as reason is concerned, the only rational concept is that of one God. Everything else is irrational. No valid argument exists in its favour. As one reads the book, one is able to comprehend the concept of God.