What does John 18:29 mean?

So far as the Roman Empire is concerned, their appointed governor, Pontius Pilate, is the man in charge of Jerusalem and the surrounding regions. For Jesus' enemies to complete their plans to have Him killed (John 11:49–53), they need the governor to issue a death sentence. He won't do that for merely breaking Jewish religious traditions (John 18:31), so the scribes and Pharisees need to cast Jesus as an insurgent against Rome.

In the most literal sense, Jerusalem's religious leaders will fail to convince Pilate that Jesus is guilty of rebellion (Matthew 27:18). However, they will use a crowd, threatening to riot (John 19:12–15; Matthew 27:24), to coerce him into executing Jesus (John 19:16).

Pilate comes outside to speak with the Jewish leaders because they refuse to enter a Gentile's home—fearing ceremonial contamination (John 18:28). The mutual contempt between the governor and Jewish leaders is on full display in this exchange. History indicates Pilate was not popular—either with Jews or with Roman politicians—thanks to his heavy-handed and violent style. Some scholars think Pilate had been threatened with discipline if he was involved in another ugly incident in Jerusalem, which contributed to his cowardly choice to execute Jesus.