What does Luke 23:40 mean?
Jesus is crucified with two thieves, one on either side of Him. Apparently, they both began the experience by heckling Him, taking their cues from the people, leaders, and soldiers who mock Jesus (Mark 15:29–32). One thief continues (Luke 23:39).The other thief reconsiders. He starts with a realization: God is to be feared. Whatever choices brought them to commit the crimes they did no longer matter. Whatever abuses the Romans have committed against the Jews no longer matter. God is God and His authority and power are to be respected. He then applies that truth to their situation: he and the other thief deserve what they are experiencing. We don't know what they did, but it must have been serious (Luke 23:41).
Next, he sees the difference in Jesus' situation: He is innocent (Luke 23:41). He has done nothing wrong to deserve crucifixion. If God is to be feared and they deserve to be crucified, how could they ridicule an innocent man receiving the same punishment? It is a mockery of God's justice and authority.
The first thief cries out, "Are you not the Christ? Save yourself and us!" (Luke 23:39). The second thief understands they don't deserve to be saved. And if the first thief is wrong about that, maybe he's wrong about the first part, too. Maybe this is the Christ!