The second criminal inadvertently summed up the core of the Gospel in his words: “we indeed are suffering justly, for we are receiving what we deserve for our deeds; but this man has done nothing wrong. Jesus, remember me when You come in Your kingdom.” (Luke 23:41-42, New American Standard Bible).
The lesson is A.A.A.: He admitted that he was a sinner. He acknowledged that Christ was the sinless. He asked Jesus the Messiah to remember him in His kingdom. He was admitted into Paradise due to his humble confession. That’s the Gospel message of Jesus Christ.