[…] There exists now, and always has existed and will exist, God, a spirit, that is, a non-embodied person who is omnipresent. […] In essence, to say that God is not embodied is to deny that there is any volume of matter such that by his basic actions he can control only it and such that he knows of goings-on elsewhere only by their effects on it. By contrast, to say that God is an omnipresent spirit is to say that he knows about going-ons everywhere without being dependent for that knowledge on anything, and can control by basic actions all states of affairs everywhere (in this or any other universe) without being dependent for that power on anything.
God is creator of all things in that for all logically contingent things that exist (apart from himself) he himself bring about, or makes or permits other beings to bring about, their existence. He is, that is, the source of the being and power of all other substances. He is, for example, responsible for the past, present, future existence of material objects and of the natural laws that they follow, of persons and their powers. And whatever else logically contingent there may be – devils and angels, and other universes – he makes them exist and behave as they do, or sustains in other beings the power to do so.
[…] God is omnipotent in the sense (roughly) that he can do whatever it is logically possible that he do. The qualification in the last clause is important. There are some apparent states of affairs, the description of which involves a logical contradiction – for example, me existing and not existing at the same time. God cannot bring about such apparent states, not because he is weak, but because the description “me existing and not existing at the same time” does not really describe a state of affairs at all, in the sense of something that it is coherent to suppose could occur…
From chapter 5 of The Existence of God, 2nd edn., revised (Oxford; 2004) see pp. 93-101, 106, 108-109 for full.