What does Mark 15:4 mean?

Pilate doesn't care if Jesus broke a Jewish religious law. And, he knows the civil accusations the Sanhedrin brought against Jesus are false. John's Gospel contains a key detail explaining Pilate's reaction in this passage: Jesus explains that He is King of the Jews but His kingdom is not on earth (John 18:33–36). By this, Pilate understands that Jesus is not a threat to himself or Caesar. Pilate knows that envy, not honor for the Roman Empire, motivates the Sanhedrin members to have Jesus killed (Mark 15:10). He does not want to execute Jesus, but he can justify having Jesus killed if not doing so would threaten peace, and he has no pressing reason not to. So Pilate asks Jesus to defend Himself.

One of the more puzzling prophecies about Jesus is found in Isaiah's description of the Suffering Servant: "He was oppressed, and he was afflicted, yet he opened not his mouth; like a lamb that is led to the slaughter, and like a sheep that before its shearers is silent, so he opened not his mouth" (Isaiah 53:7). Obviously, during the trials before the crucifixion, Jesus does speak. He challenges the legality of the Sanhedrin trial and affirms His identity as the Christ (Mark 14:53–62). Later, He has a conversation about His kingdom and the nature of truth with Pilate (John 18:34–38). How is this "remaining silent?"

The key is in what Jesus speaks about. Jesus is silent in His defense. He speaks, but never says anything that would delay His path to the cross. He shouldn't have to, as all the accusations are false. But the fact that He refuses to defend Himself against false accusations, and that the members of the Sanhedrin are so aggressive, leads Pilate to think he has no choice but to give the mob what they want.