Aristotle's theology is the last step of a physical argument, not the first step of a devotional one. Everything that moves, he holds, is moved by something; an infinite regress of movers explains nothing; so there must be a first mover that is not itself moved. Book twelve of the Metaphysics works out what such a thing would have to be. It cannot be made of matter, because matter carries potential and a first mover must be wholly actual. It cannot change, because change is the thing it exists to explain. It cannot act on the cosmos by pushing, because pushing would be a motion in it, so it moves the outermost sphere as an object of desire moves the one who desires, by being loved rather than by doing anything. And since the best activity available is thinking, and it can have nothing better than itself to think about, it is thought thinking itself.
What follows from that is as important as the argument. This god does not make the world, which for Aristotle has always existed and always will. It issues no law, hears no prayer, and knows no particulars, because knowing changing things would change it. It is not one of the gods of the city, and Aristotle nowhere suggests that anyone should worship it. Readers who wanted a creator, a lawgiver and a listener had to argue their way from this figure to that one, and the difficulty of doing so is most of medieval philosophical theology.