What does Mark 15:30 mean?

To any other crucifixion victim, this would be a cruel taunt, something they could never do. To Jesus, it's a legitimate temptation. But Jesus has dealt with the same temptation before.

During Jesus' forty days in the wilderness, Satan tempted Him to save Himself by making bread and manipulating the angels into taking care of Him (Matthew 4:1–7). Jesus rebuked both temptations with a combination of Scripture and reverence for God. Then, Satan offered to give Jesus dominion over the world without the cross (Matthew 4:8–11). During the guards' torture, they dress Jesus as caricature of a vassal prince (Mark 15:17), the same position Satan offered Him. Had Jesus taken Satan's offer, humanity would have been condemned forever.

Satan also used Jesus' disciples to tempt Him. When Jesus first revealed He will be rejected and killed by the Jewish leadership, Peter had the audacity to deny Jesus' words (Mark 8:31–33). Jesus called Peter's words satanic. When Judas brought the guards to the garden of Gethsemane, and Peter drew his sword to strike a servant of the high priest, Jesus stopped the attack (Matthew 26:51–52). He told Peter, "Do you think that I cannot appeal to my Father, and he will at once send me more than twelve legions of angels? But how then should the Scriptures be fulfilled, that I must be so?" (Matthew 26:53–54).

It would have been the stuff of a Hollywood movie for Jesus to suddenly free Himself from His bonds and take vengeance on His accusers and abusers. But that is not why He came. He came to obediently hang on the cross (Philippians 2:8), to seek and save the lost (Luke 19:10), to lay down His life for the sheep (John 10:11). He does so voluntarily (John 10:18). His reason for coming to earth as a man is only a few hours from completion. He's not going to stop now.