It's been said many times before. A Christian will ask an atheist what he will say on judgment day to God if, in fact, the atheist was wrong. The atheist replies, "I will say that He did not give me enough evidence to believe in Him." In other words, the atheist did not empirically verify enough evidence for God that it made him believe in Him. There was no experience, where the atheist could see with his own eyes that God existed as a Personal Being in whom one should place his faith.
There are other atheists who demand God strike them down in front of crowds as proof of His existence, and others who just say that if He really existed, and wanted everyone to believe (something many of us as Christians don't believe in terms of His decree, even if it is in accord with His moral/revealed will), then He would just come down from heaven and appear to everyone so that every man could plainly see Him and believe.
The problem with this, of course, is that God requires faith rather than sight in order to have a relationship with Him. The atheist believes that this is the case because God doesn't exist, so saying He requires faith is a way to cover up the fact that He can't appear to everyone as a nonexistent being. Theists are just making excuses for their made up deity.
The Christian, however, believes that God requires faith because there is something necessary about it. Hence, to appear to everyone, or make Himself known by evidence beyond a reasonable doubt, is to negate what is a necessary condition of having a relationship with God in the first place. To do so would mean that God would appear to everyone and come into a relationship with not a single one of them.
But what is the reason that faith is so necessary? The answer is our sin, our tendency to commit idolatry and worship the Self instead of God. This is the very reason why we can't use graven images to commune with God. We can just pay tribute to a visible god in front of us, but carry on unchanged by the encounter. We remain corrupt because the wayward worship of the Self as God and Savior remains intact, as the Self was never internally submitted to another Lord, since it demanded to see God and its commands were obeyed as though it is god. Visible confirmations of deity allow us to hold onto the Self and all of our own pursuits. They don't demand any relinquishing of the Self. Hence, their worship is only external and nontransformative. There is no submission from the inside out to God. In fact, demanding that we see for ourselves is an act of rebellion, not faith, that demands that God meet our criteria in order to believe in Him, which of course is no belief at all. Faith, however, is an act of submission. It is an act where we allow God to demand of us without the god of Self having to be master over the situation, master over the relationship, governing its stipulations.
This is why demanding some personal experience with God before one will believe that He is and that He has spoken in His Word is at such a conflict with true faith. It builds rather than destroys self-reliance and idolatry, and works against a relationship with God where we rely upon Him as God, our only true source of life and eternal salvation.
We need our lives in God. Outside of Him we become corrupt and corrupt others in falsehoods and evil. Outside of Him, there is no true life at all. Therefore, we need to enter into a relationship with Him. We were made to worship, but we have distorted its object, and have thus died in doing so. He is our only hope back to life, and therefore, faith is our only hope, because it denounces the Self and its demands that God capitulate to it, and trusts in God instead.
You see, faith must be transferred from the Self to God in order for us to be restored to life; but if God just shows up or proves Himself beyond a reasonable doubt, we cannot have faith then. God has killed us by doing this rather than having saved anyone. And He seeks to save, not destroy what was lost.
Hence, faith cannot be had by sight; and because faith is necessary for us to be saved (it is the beginning and end of the process of our salvation, as it is an essential component to deny the demands of Self and both enter and remain within a relationship with God as our God), it cannot be set aside if we are to enter into a genuine submissive relationship with God.
What the atheist, or anyone else who demands that God prove Himself or what He has said in Scripture beyond a reasonable doubt, is really asking of God is that God damn them to themselves, not save them from themselves. But God doesn't need to appear or prove Himself in order to do this, as they will not believe, they are damned to themselves already. Mission accomplished.
The atheist, or anyone else who will not believe unless he sees for himself, is left with the Self as Lord, and hence, is left with the Self as Savior (I've said before, Christ can be our Savior only because He is our Lord, and since He is saved, all that He owns as Lord is saved with Him). The Self cannot save anyone, so whoever exalts it will surely be damned in the end.
God, therefore, makes enough provisions in the world and in the Scripture for anyone to believe and enough for him to disbelieve. He provides both, as one can only exist with the possibility at some point of the other. If faith is to exist, doubt must also be a possibility. Hence, God cannot appear or make Himself known beyond all reasonable doubt without destroying all of mankind by leaving it to itself as its own deity.
We can apply this to biblical interpretation as well. Do you need to experience what God has said is true and good before you believe it in His Word? Then you are seeking a life of Self and the damnation thereof in the rejection of faith. Faith must seek understanding, not vice versa. The false god of Self demands that everything submit to it as Lord, including God, but that is not of faith, and therefore, it is not the road to life and salvation.
So God isn't going to strike you down in a crowd to prove Himself. He isn't going to show up in Times Square on New Years Eve. He's not going to show up in your bedroom so that you can start believing the Bible He gave to you. And He is not going to verify in your experience everything He has spoken in His Word so that you'll finally believe it's true. Christianity isn't confirmed by sight because it isn't a religion of the Self, so God isn't going to feed the fire of Self by showing up and proving everything to His people. He loves His people too much for that. He actually wants to save them. As the Scripture says, "Faith is brought about by hearing, and hearing [is brought about] by the Word of God." If you want to know that God is and that He gives life to those who seek Him, you must believe; for that is the only course possible for one to take in order to be saved from the greatest, most corrupt, and deadliest tyrant of all, the Self.