"But Thomas, one of the twelve, called Didymus, was not with them when Jesus came. The other disciples therefore said unto him, We have seen the Lord. But he said unto them, Except I shall see in his hands the print of the nails, and put my finger into the print nails, and thrust my hand into his side, I will not believe. And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be with you. Then saith He to Thomas, Reach hither thy finger, and behold My hands; and reach hither thy hand, and thrust it into my side:and be not faithless, but believing. And Thomas answered and said unto Him, My Lord and my God. Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed." John 20:24-29
The unbelieving world has already seen Jesus, just like Thomas; they have already been a recipient of God's prevenient grace; they have already seen the mighty works of the hand of God and in their own lives they have received countless blessings because of the prayers and intercessions of others. But, just like with Thomas, it is not enough. They want more proof. I've heard it all:
If Jesus was real, why do young people die before their time?
If Jesus was real, he could put a stop to all the pain and suffering of the world?
If Jesus was real why did he let this or that happen?
If I saw a miracle I would believe.
If Jesus was to come and talk to me personally I would believe.
If Jesus was to give me this or that I would believe.
One thoughtful moment spent in cogitating on creation, the birth of a child, a rose, the mountains, our rivers, a glance into the stars, and a thoughtful counting of the many blessings that have come our way is all the proof anyone would need.
Jesus said, "blessed are they that have not seen, and yet have believed." The atheist, the agnostic, and those who have been conditioned to believe in another god; all are fighting their own inner unction that God placed in them to seek and find the One true God. Thomas believed once he saw the hand prints and the spear mark, but not everyone believed.
There were many that walked right along side of Jesus and ate with Him and sat under His teaching and yet held onto their religious dogma or in some cases irreligious hedonism. Either way, coming to Jesus is through faith and does not require sight, nor does it require that you or someone else perform a miracle, nor does it require that Jesus walk on water again to prove Himself.
The best proof you can offer anyone is your personal testimony of your own faith. Does your personal testimony include , "My Lord and my God?"