The first subject of any apologist must be the existence of God. For if there is no god, all religion is merely part of the population manipulating another part to some end. If there is no spiritual dimension, no metaphysicial reality then there is only nature: the observable world and religion is simply a vain affectation. Certainly many who hold themselves to be scientific embrace this view.
First, I maintain that there is a metaphysical reality. I hold this view for several reasons. There is a universal acceptance of the spiritual sphere. Not that every person in the world holds this for they do not. Rather that every people group in the world is religious. Perhaps I had best pause and define religious as: of or relating to the worship of or a doctrine concerning a divine being or beings (from the New Oxford American Dictionary.) It is apparent that by this definition even atheism is a religious belief! Every tribe and nation believe in some kind of religion. Spirituality is ubiquitous. Surely if this were merely human invention it would not have been invented everywhere by everyone. Think of how the wheel and alphabet are not ubiquitous. But religion is universal. In contemporary America as we have become more “scientific” (i.e. more convinced that evolution is true and there is no supernatural world) in reality we have become increasingly superstitious. There has never been more belief in angels, demons and ghosts since the middle ages.
Second, if there is a spiritual dimension either it is either inhabited or not. If it is not inhabited by beings (other than whatever spiritual dimension we may possess) then it is of no concern to us. If however it is inhabited then we must be concerned with the beings that live there as they undoubtedly have power to influence our natural world.
Third, what do we can a superhuman being? The New Oxford American Dictionary defines god as: a superhuman being or spirit worshiped as having power over nature or human fortunes. So if there is a spirit world and it is inhabited at least some of it's inhabitants may properly be called gods according to our understanding. Again, if these beings have no power over nature or human fortunes than they are not gods and we need not concern ourselves with them.
Fourth, the existence of God. If there are 2 or more gods then relating to one or all of them may be problematic. What if we relate to a god who is overpowered or destroyed by another god? What if we worship a god who is capricious or untruthful? What if the gods interfere with each other's revelation of themselves to us? In pluralistic deity there can be no sure relationship with any divine person and hence we are hopeless to discern a right and wrong way to relate to such a reality.
So if there is a metaphysical world inhabited by a being of power that necessitates the existence of God. A God powerful enough to create the world and reveal Himself to us. A God righteous enough to truthfully reveal himself and just enough to rule over and administer the world fairly. Thus I posit the existence of one God against all forms of atheism, naturalism, pantheism, polytheism and dualism.