What does John 18:25 mean?
Once again, John employs a "scene change" that almost mirrors techniques used in modern films. Previous verses explained how John and Peter followed the squadron arresting Jesus, entering the outer courtyard of the high priest (John 18:12–16). During that passage, Peter's earlier bragging (John 13:37) and reckless bravery (John 18:10) gave way to a self-preserving lie (John 18:17–18). The focus then shifted to Jesus, being interrogated by Jewish religious leaders (John 18:19–24).Here, again, John "cuts" back to the outdoor courtyard, where Peter is standing with John and several strangers. Once again, he is questioned about his relationship with Jesus. Matthew explains that Peter's Galilean accent makes him stand out (Matthew 26:73). The question here is being asked in a way which expects a negative answer. To sneak into the high priest's courtyard while their master is being tried would be foolish, after all.
Just like he did with the doorkeeper, Peter lies and claims he is not a follower of Christ. This is as Christ predicted earlier in the evening (John 13:38).
Even worse for Peter, one of the men standing at the fire was an eyewitness to Jesus' arrest. In fact, the man is a relative of the person Peter maimed in his effort to defend the master he now denies knowing (Luke 22:50–51; Matthew 26:51; John 18:10).