This is one of my favourite essays on the subject of morality and God. It is by P. Wesley Edwards and can be found variously online, such as here. JohnM was espousing the idea in his comments here that under an atheistic worldview, there is no moral foundation. Moreover, as the argument goes, only God can provide a sound underpinning for morality. In this essay, Edwards shows how this tack is circular and thus incoherent. As ever, let me know what you think.