[Introduction] Why believe that there is a God at all? My answer is that to suppose that there is a God explains why there is a world at all; why there are the scientific laws there are; why animals and then human beings have evolved; why humans have the opportunity to mould their characters and those of their fellow humans for good or ill and to change the environment in which we live; why we have the well-authenticated account of Christ's life, death and resurrection; why throughout the centuries men have had the apparent experience of being in touch with and guided by God; and so much else. In fact, the hypothesis of the existence of God makes sense of the whole of our experience, and it does so better than any other explanation which can be put forward, and that is the grounds for believing it to be true. This paper seeks to justify this answer; it presents in summary arguments given in more detailed form in my book The Existence of God,[1] and seeks to rebut criticisms of those arguments given in J.L. Mackie's book The Miracle of Theism.[2]