In the book of Luke 23:39-43, The thief on the cross is the criminal that was crucified along with Jesus who repented at the last moment, he rebuked the other thief for mocking Jesus, one mocked him and the other defended him, he also acknowledge that they were receiving deserved punishment and said that Jesus has done nothing wrong, the one that defended Jesus told him to remember him in his kingdom, then Jesus promised him that he will be with him in paradise that day.
This story is a powerful example of the last minute salvation, the thief salvation was not earned through his work, not by baptism, or any other sacrament, but a gift from God through his faith in Jesus.
Even during his last moment, he was able to turn to Jesus and find forgiveness, that tells us that is never too late to repent and accept salvation.
You can demonstrate God's grace even at the end of your life.
The thief acknowledged his own sin and deserved punishment, he showed humility and repentant heart that led to his redemption.
He believed in Jesus identity as a king, and trusted him with his eternity, which tells us that faith in Christ is the right way to salvation.
No sin is greater than God, the story thought us that even a long term of sin does not prevent God from offering salvation to those who turn to him in faith.
The thief knew that he was a criminal, and can't enter heaven because of his own merit, he rely solely on Jesus grace, telling us that salvation is not dependent on someone's past life.