"Proof" does not apply, when it comes to the spiritual realm. The standards and laws of the spiritual world are completely different from those on Earth, in the physical realm. You cannot prove, what you cannot see. However, just like the wind, you know it's there and you know it's real, though you cannot see it....you can see the effects of it, but not the source. The same applies to God. Not everything that is real in this world, can be seen. That does not mean it does not exist. There are the tiniest tiniest microorganisms that men cannot even see through a microscope, yet they live. Look at the people who don't believe in God because they can't see him, yet are hiding out in their homes from a virus they cannot see, but they believe is there. Why? Because they saw the effects! Yet they can't believe in Almighty God? Not even after seeing His beautiful handiwork in the heavens? He....who holds the stars in place? We don't need proof, we need faith.
However, there is another side to that coin. Jesus came to Earth and already proved himself and look what happened! He was rejected and hung on the cross for it, so why would he want to expose himself to that again, when he completed his mission to save mankind and then went back to his Father in Heaven?
Since He is now invisible and His abode is in the spiritual realm, that's why it requires faith. Yet it is not a faith in vain, because he left his fingerprints on everything. Are we so blind that we cannot see his handiwork in everything around us? We see Him in all of nature, in the miracle of a birth, in the animals, in the beauty of the flowers and trees, and in the whole universe. Or, are we spiritually blind? I don't know how anyone could miss it. He even left his Holy Word, so that we would not have to guess how to get to heaven. Then we still complain it's not enough, even after he shed his precious blood on the cross to pay for our sins. There's nothing more Jesus could have done for us. He gave us his very best. He gave us his very life. I could not be more grateful to him. If it had not been for his great sacrifice, we would have all gone to hell. Would we have preferred this scenario? I think only a foolish person would accept that, over heaven.
God made His physical appearance once and that's all it took to save mankind, if he will accept God's gracious gift of salvation. Once, was quite enough. He didn't have to come to save us, but He did. In fact, He volunteered. Proving, how much he loves us.
