What does John 18:39 mean?

History offers little detail about the custom Pilate mentions here. What's more relevant is the fact that Pilate is actually trying to have Jesus released. After a private interview (John 18:33–38), it's clear Jesus is innocent of any crime against the Roman Empire. Accusations of sedition are false (Luke 23:2), and the real problem is a personal vendetta (Matthew 27:18; Mark 15:10). Luke notes that Pilate even sent Jesus to Herod, hoping someone else would be responsible (Luke 23:6–12). He will go so far as to have Jesus brutally whipped and humiliated (John 19:1–4), hoping to appease the situation, but it won't work.

As the governor, Pilate could simply refuse to judge Jesus. History suggests reasons why Pilate is being weak-willed. The Roman Empire was mostly concerned with keeping the peace in conquered territory. Pilate was known for his harsh, overly violent approach to the Jews, resulting in a mutual disrespect (John 18:30–31, 35). His remark about Jesus being "King of the Jews" is a deliberate attempt to rub Israel's face in Roman rule, and to tease the scribes and Pharisees about their views of Jesus. History records a few incidents where Pilate's aggressiveness and antagonism towards Jews threatened to create even more unrest. Scholars suggest Pilate had been told by his superiors that another ugly incident would result in being removed from his position.

Now, Jesus' enemies have assembled a mob (John 19:12–15), which will threaten to riot (Matthew 27:24). This is occurring near one of the holiest days in the Jewish year (John 18:28), and Jerusalem is swarming with passionate, observant Jews. The combined accusations of blasphemy (John 19:7) and rebellion make the crowd's demands volatile.

Ultimately, Pilate will cave to pressure, setting aside his moral principles (Matthew 27:24) to appease an angry mob. In a display of blatant hypocrisy, he will also release someone known to be guilty of the very crimes Jesus' enemies claim (John 18:40; Luke 23:18–19).