People often say things like "If God is real, then why doesn't He show us?"
Well, He did ... it's called Creation.
"No, no, that's just evolution. It's nature," they reply. "But if He was really real, then why doesn't He send us a clear message, in black and white?"
He did ... it's called the Bible.
"Oh, that was just written by men. It's an interesting old book. Nothing more. But if He was really, really real, then why doesn't He come down here and show Himself to us physically? Because then we'd believe."
Once again, He did ... and His name is Jesus. And they still don't believe.
"For since the creation of the world God's invisible qualities - his eternal power and divine nature - have been clearly seen, being understood from what has been made, so that men are without excuse." (Romans 1:20)
"But these are written that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name." (John 20:31)