What does Mark 14:31 mean?

Peter fulfills his vow, but not for several decades. John 13:36 says, "Simon Peter said to him, 'Lord, where are you going?' Jesus answered him, 'Where I am going you cannot follow me now, but you will follow afterward.'" After the crucifixion and resurrection, Jesus tells Peter, "…when you are old, you will stretch out your hands, and another will dress you and carry you where you do not want to go" (John 21:18). Jesus predicts that Peter will, indeed, follow Jesus to death, and death on a cross. Church tradition says that John, who was listening in on Jesus' words to Peter, died of old age, but Peter was crucified. That same tradition says Peter opted to be crucified upside-down because he didn't consider himself worthy to die in the same way as his Lord.

Mark is not one of Jesus' twelve disciples, although it's possible he is with them on the Mount of Olives (Mark 14:51–52). It's believed Mark got most of his information from Peter. If so, this passage and its fulfillment in Mark 14:66–72 emphasize how a great change came over Peter. Here, he is brash, contradicting Jesus as he has done before (Mark 8:31–33). Soon, when Peter denies that he knows Jesus, his "courage" will prove to be empty arrogance. Later, however, after Peter receives the Holy Spirit (Acts 2:1–4), his strength will come from God. He will preach to thousands in the middle of Jerusalem (Acts 2:14–41) and in the temple courtyard (Acts 3:11–26). He will feel honored to be imprisoned and beaten, grateful that God finds him worthy of suffering in the name of Jesus (Acts 5:17–42).

Peter's transformation is a powerful testament that our hearts can only be truly changed by the power of the Holy Spirit. We may claim to be brave, loyal, and willing to die for Christ, but without the Holy Spirit, we are merely looking out for ourselves (Romans 3:12).