If you've talked with atheists long enough you'll have heard the demand, “Jesus should just show Himself to me and then I'd believe.”
A materialist would not believe.
S/he would simply come up with a materialist explanation for why Jesus seemed to suddenly appear.
Aside from that fact, I'm glad that God has not appeared to us. I'm glad that He has done nothing more than reveal Himself to those who genuinely search for Him. I think it was Pascal who said something like, “God has given us just enough evidence of Himself, so that those who are destined to be saved will be able to find Him, while those are going to reject Him will not be able to find Him accidentally.”
I think this hiddeness of God is actually a sign of His love. For if God showed Himself to us. If God made His existence crystal clear, then any rejection of Him (and there would still be rejection – ask any atheist) would be ultimate and final. There would be no possibility of redemption for that type of rebellion. For then we would have maximum revelation, Maximum light. There is no turning back from that kind of rebellion.
In His love, God knows that our human nature resists the brute fact of His existence.
He knows that we must struggle to accept His reality.
He knows that all of us initially push away His love without which we cannot exist.
He knows who will, in time, come to desire His love and forgiveness more than anything else in the world.
Out of His enormous love, Creator God gives us time to let the weight of our sin, propel us toward His love and mercy and grace. Out of this is a Christian born.