[Originally posted at the Rational Gang. Please direct any comments there.]
A lot of atheists say that if God were to perform a miracle in front of their eyes, then they would believe. So then, if God is all good, and "wills all men to be saved," then why doesn't he provide such obvious evidence for his existence? Since an all-loving God is expected to reveal himself to all, and there are atheists that have reasonable nonbelief, this is evidence that God does not exist.
1. Coercion and Moral Responsibility:
A first thing to note is that God wants to preserve our moral responsibility and freedom. Now, almost all accept that it is possible to coerce someone into doing something. This can be done, most obviously, by physical force, as when kidnappers pick up a hostage and put him into a van against his will. Clearly in this context the person is not responsible for this event. Another, more interesting case, is where a mother is forced by a cruel killer to choose between her two sons being shot, or else they will both be tortured to death. The mother is not morally responsible, or at least very responsible, if she ultimately chooses one child in order to save at least one; the ultimate responsibility goes to the wicked sadist who is forcing the "choice" upon her. The point here though is that the mother is not literally coerced by force; rather, she is coerced by reasons. She knows that if she doesn't pick one, they will both be lost. In cases of coercion, one loses moral responsibility for one's actions.
But then it's straightforward applying this to the case of God. God wants us to have the freedom to choose him. He doesn't want to coerce us and ultimately remove our responsibility. But if one can be coerced by reasons, and incontrovertible proof would coerce some people into belief, then it's easy to see why God would not provide incontrovertible proof to absolutely everyone in order that they might all have absolute certainty: It removes responsibility on our part.
2. Divine Obviousness:
A reply inspired by the Thomistic tradition is to say that, as a matter of fact, God isn't hidden at all. Rather, God, as the ultimate source of all being, completely and totally permeates throughout nature. This is how God is omni-present, not in the sense that the universe is God (a la pantheism), but rather that the very existence of things is just one step away from God himself. However, being creatures of habit, and being familiar with the world, we take the awful mystery of existence for granted, and fail to see the divinity which sustains it all. But this is no failure on God's part. It's a failure of us to appreciate God's creation.
3. They're Wrong:
While atheists say they know that if God were to provide them a clear sign such as a miracle then they would convert, that might, for all we (or they) know, not be the case. In fact, this is what we find from the Christian perspective in John 11, where the Pharisees, even upon hearing and accepting that Christ performed miracles, refused to acknowledge him: "So the chief priests and the Pharisees gathered the council, and said, 'What are we to do? For this man performs many signs. If we let him go on thus, every one will believe in him, and the Romans will come and destroy both our holy place and our nation.'" So for these people, even the greatest of miracles would not convince them. How would this apply in the case of others?
According to one theory of the relationship between God's foreknowledge and our freedom, Molinism, God knows infallibly what we would freely do in any given circumstance. Supposing this view is coherent, we can apply it in the case of atheists: God does not give incontrovertible evidence to people who he knows that, in any circumstance where they are given incontrovertible evidence, would not convert. This means that atheists cannot say, "Well, if only God had given me more evidence, then I would have converted." Not necessarily.
If this is too strong, we can even weaken the principle: God does not give reasonable evidence to people who he knows that, in any circumstance where they are given reasonable evidence, would not convert. This seems more plausible anyway. For one, it doesn't seem necessary for God to give everyone incontrovertible evidence. If we are given reasonable evidence and fail to see it, then that is our fault. Moreover, this widens the group of people we are dealing with because, though some may accept God given incontrovertible evidence, fewer will accept God given only reasonable and sufficient evidence, which may explain a large number of unbelievers.
What this ultimately shows is that, even if some atheists are not actually given incontrovertible, or even reasonable, evidence, this doesn't make it the case that God is doing something evil, the reason being that they would not accept the evidence in other feasible circumstances anyhow. It would be for God to cast pearls to swine.
4. Rationality and Reasonableness:
This leads to a further question: are atheists, in fact, given reasonable evidence? Their whole argument may be begging the question here. After all, theists believe that there is reasonable evidence for the existence of God. But then if God has provided everyone with reasonable evidence, the argument fails, because this is precisely what is in question, i.e. whether belief in God is reasonable.
The atheist finds himself in a bit of a pickle. In proposing that there is not enough evidence for Christian belief, he must give us a criterion of reasonable belief that is strong enough such that it supports the reasonableness of atheism, but is not so strong that it begs the question against the theist. To put it another way, there is a tension in the claim that "the reasonableness of atheism entails the unreasonableness of theism," because it is possible that, given the atheist's criterion of reasonableness, the theist can turn right around and say, "Well, it is reasonable to believe that God might not reveal himself to everyone with absolutely convincing evidence."
5. Five points.
To sum up, I think there are five reasons we can give as to why God's existence is not incompatible with "divine hiddenness."
(a) Reasons can coerce. So if one were given incontrovertible reasons to believe in God, then one would be coerced into belief in God. But since coercion is incompatible with significant moral responsibility, and God wants to leave us morally responsible, God does not want to coerce us. Therefore, God does not give incontrovertible evidence.
(b) God is not in fact hidden; rather, God is obvious. However, humans fail to recognize the mystery of their own existence and the creation before them, and fail to see the divine in nature.
(c) For all we know, God does not give those who have a reasonable non-belief in God incontrovertible evidence, because he knows that in all circumstances, they will not believe in God.
(e) For all we know, God does not give those who have a reasonable non-belief in God reasonable evidence, because he knows that in all reasonable circumstances, they will not believe in God.
(e) The atheist begs the question against the theist in two ways: first, by saying that his nonbelief in God is reasonable, since the theist believes there are reasonable grounds for belief, and second, by saying that his reasonable nonbelief implies God's nonexistence, since the the theist can say that, by the atheist's own criteria, it is reasonable to believe that God has reasons to stay hidden.
All in all, this provides a strong cumulative case for believing that the argument from divine hiddenness doesn't work, and that theism is left unharmed.