For the assertion that "There is no God" is just as much a claim to knowledge as is the assertion that "There is a God." Therefore, the former assertion requires justification just as the latter does.
William Lane CraigThe way in which I know Christianity is true is first and foremost is the basis of the witness of the Holy Spirit in my heart. And this gives me self-authenticating means of knowing Christianity is true wholly apart from the evidence. And therefore, even if in some historically contingent circumstances the evidence that I have available to me should turn against Christianity, I do not think that controverts the witness of the Holy Spirit.
William Lane CraigAtheists themselves used to be very comfortable in maintaining that the universe is eternal and uncaused. The problem is that they can no longer hold that position because modern evidence that the universe started with the Big Bang. So they can't legitimately object when I make the same claim about God - he is eternal and he is uncaused.
William Lane Craig