What does Mark 14:42 mean?

During the Passover meal Jesus dismisses Judas (John 13:27). The disciples think Jesus has sent Judas to buy supplies for the Feast of Unleavened Bread to be celebrated the next evening (John 13:28–29). In fact, Judas has gone to the Sanhedrin to collect guards to arrest Jesus.

"Betray" is from the Greek root word paradidomi. It infers a position of authority that allows the betrayer to treacherously place the victim in a harmful situation. Judas is almost always named in the context of his betrayal of Jesus. He is the "son of destruction" (John 17:12). "Destruction" is from the Greek root word apoleia which describes the misery and utter ruin that occurs in hell. Jesus chose Judas as a disciple knowing Judas had the character to betray Him.

Today, we would call Judas an especially fiendish type of apostate. An apostate is someone who understands Jesus and the gospel but utterly rejects them. Jesus notes the difference between a weak follower and a strong enemy. Peter will deny he knows Jesus, but Judas is here to betray Jesus. Peter believes in Jesus' authority and waits for Jesus to give him what he wants (Mark 9:33–34). Judas believes in money and hands over Jesus to get what he wants (Matthew 26:14–16). Peter will recover, accepting forgiveness from Jesus and spending the rest of his life in Jesus' service. Judas will awaken to the weight of what he has done and choose the only permanent alternative to Jesus' forgiveness: death without faith (Matthew 27:3–5).