What does Mark 15:11 mean?

The chief priests are trying to get the Roman government to execute Jesus. The Jewish leaders have tried to kill Him on their own but failed (John 7:32; 8:59; 10:31–33). This is not an ideal time to attack a popular man (Mark 14:1–2). Jerusalem is bursting at the seams with Jews who have come for the Passover and the Feast of Unleavened Bread. Many of these travelers are from Galilee, where Jesus is from and where He has a strong following.

The chief priests and other members of the Sanhedrin, the Jewish ruling council, have justified their murderous intent to themselves by convicting Jesus of blasphemy against God (Mark 14:61–64). But they need a reason that will resonate with the Roman governor, Pilate. They're apparently unaware that far from seeing it as blasphemous, Pilate fears that Jesus' claim to be the Son of God might have some element of truth, making him even more reluctant to execute Jesus (John 19:6–8).

To convince Pilate that Jesus is a threat to Rome, they claim Jesus is planning an insurrection (Luke 23:2). When both Pilate and Herod Antipas—the tetrarch of Galilee—are skeptical of that accusation (Luke 23:14–15), the chief priests resort to the same thing they accuse Jesus of: they threaten a riot.

Barabbas is described as an insurrectionist and a murderer (Luke 23:19). Ironically, such qualities better represent who the Jews expect the Messiah to be. They look for a warrior-king to lead the people into battle against the Roman oppressors. They don't expect a poor teacher who intends to let Himself be killed for the sins of the world. Barabbas has proven he can fight. Jesus just made fish and bread feed a multitude. That's no longer enough (John 6:11–15, 26). The Jews think that they have chosen to let Barabbas live instead of Jesus. They don't understand Jesus has chosen to die for Barabbas.

We don't know who this crowd is comprised of. It is morning of Passover. The Galileans ate the night before, and the Judeans should be preparing to sacrifice their lambs that afternoon. The people who declared Jesus' entry into Jerusalem was the return of the Kingdom of David were likely a small portion of the travelers from Galilee, Decapolis, and Perea; they most likely weren't residents of Judea. It's very possible that this crowd, one the chief priests have riled up, knew relatively little about Jesus or His ministry.