The gist of the book is this:
Christians must see the world as intelligently designed by the divine Creator, who exercises providential care over human beings and who judges them in the afterlife as deserving heavenly rewards or hellish punishments for eternity. Christians can interpret many of the ancient philosophers - Platonists, Aristotelians, and Stoics - as teaching that the world is fundamentally mindful and purposive and thus supporting a Christian cosmology. But they can't do this with the atomistic cosmology of Epicurus and Lucretius, which must be seen as the fundamental rival to Christianity.
Moreover, Wiker argues, one must defend Christian cosmology if one wants to defend Christian morality. As a comprehensive account of the universe, every cosmology implies a morality, because every account of nature as a whole implies an account of human nature - the moral and intellectual life of human beings - as part of cosmic nature.