I have been asked, "If God made the universe, then who made God?"
My response is: this is a nonsense question. It's like asking, "How much does blue weigh?"
The Christian God, the theistic Being, is understood to necessarily exist. That is, God cannot not-exist. If God cannot not-exist, then God has eternally existed. God never began to exist. If something never began to exist, it never came into being. Hence, it has no cause.
This is similar to the question, "If God is all-powerful, then can God make a stone so heavy he cannot lift?" This is another nonsense question. Here's why, in some detail.
I'm drawing upon former University of Michigan philosopher George Mavrodes's "Some Puzzles Concerning Omnipotence" (in Peterson, Hasker, Reichenbach, and Basinger, Philosophy of Religion). I heard Mavrodes speak years ago at a philosophy conference at Wheaton College (I took two independent studies with Wheaton philosopher Arthur Holmes). And once, while strolling the halls of U-M's superb philosophy department, I walked into Mavrodes's office as his door was open. He was very gracious, and we talked a bit.
If God is "omnipotent," does this mean God can do anything? Can God create a stone too heavy for him to lift?
It's generally understood that the doctrine of omnipotence refers to the ability to do anything that is logically possible. So, e.g., God cannot make a "square circle," simply because such a thing is logically incoherent.
While "square circle" "seems plainly to involve a contradiction..., [the statement that] "x is able to make a thing too heavy for x to lift" does not." (141-142) I could, e.g., make a boat too heavy for me to lift. Why, then, could not God make a stone too heavy for him to lift? At least, it's not obvious that such a thing is logically incoherent, in the sense of being self-contradictory or even meaningless.
With this in mind, Mavrodes argues that the stone-idea is self-contradictory in the same way as is "square circle." Here's how this works.
God is either omnipotent or he is not. If he is not omnipotent, then the phrase "stone too heavy for God to lift" may not be self-contradictory. It follows that if God can make such a stone, then he is not omnipotent. But if we assume that God is omnipotent, then the phrase "stone too heavy for God to lift" becomes self-contradictory. "For it becomes 'a stone which cannot be lifted by Him whose power is sufficient for lifting anything'. But the "thing" described by a self-contradictory phrase is absolutely impossible and hence has nothing to do with the doctrine of omnipotence." (142) "The very omnipotence of God... makes the existence of such a stone absolutely impossible, while it is the fact that I am finite in power... makes it possible for me to make a boat too heavy for me to lift." (142)
But what if someone objects and claims that "stone too heavy for God to lift" is not self-contradictory, and therefore describes an absolutely possible object?" (142) If that is correct, than our answer will be, "Yes, God can create such a stone." The existence of such a stone will then be compatible with the omnipotence of God. "Therefore, from the possibility of God's creating such a stone it cannot be concluded that God is not omnipotent... The conclusion which [the objector] wishes to draw from such an affirmative answer to the original question is itself the required proof that the descriptive phrase which appears there is self-contradictory." (142)
To the question, "Can God make a stone too heavy for Himself to lift?" the objector wants us to answer, "Yes." But if we answer "Yes," the objector will think our answer to be absurd, since the idea of a stone too heavy for God to lift is logically absurd. This is because, once we grant omnipotence to God, plus non-self-contradictoriness to the "stone too heavy for God to lift," we are involved in a logical absurdity which denies what we have granted to God. Mavrodes says: "It is more appropriate to say that such things cannot be done, than that God cannot do them." (Ib.)