What does Mark 15:20 mean?

Pilate had tried to free Jesus, or at least get out of killing Him (John 19:1–16). He presents Jesus to the roaring crowd, beaten, bloodied, brutally scourged, and wearing a crown of thorns and a mocking royal robe. The Jewish leaders won't budge from their plan to see Jesus crucified, which confuses Pilate. But what scares Pilate is their reasoning: "We have a law, and according to that law he ought to die because he has made himself the Son of God" (John 19:7). What the monotheistic Jews hear as blasphemy, the polytheistic Roman Pilate hears as a frightening possibility. What if this man is telling the truth?

So Pilate speaks to Jesus one more time, begging Him to defend Himself (John 19:8–11). Jesus asserts that neither the Jews nor Pilate are in control of the situation; God is. Jesus also slightly absolves Pilate of the crime, saying that God has placed him in this untenable position and the true criminals are the Sanhedrin members who charged Jesus in the first place.

Burdened with Jesus' refusal to defend Himself, Pilate appeals to the crowd a final time (John 19:12–15). The Jewish leadership pulls out their trump card, insisting that releasing Jesus would be a crime against Caesar. History suggests that Pilate's tenure as governor here was not well-liked by his Roman superiors. The only worse outcome than a Jewish rebellion against Caesar and Pilate would be a Jewish rebellion against Pilate in the name of Caesar. This threat hits Pilate where he is most vulnerable, so he lets Jesus be crucified.