What does John 13:30 mean?

Jesus made an emotional prediction that He would be betrayed by one of His closest friends (John 13:18–21). In response to a question from John (John 13:25), Jesus gave a subtle sign indicating that the traitor was none other than Judas (John 13:26). In the moment Jesus confirms, to Judas, that He knows about the betrayal (Matthew 26:14–16; John 13:2), Judas becomes fully possessed and controlled by Satan (John 13:27). Jesus gave a command to Judas / Satan to leave, which the other men mistook for Jesus sending him on an errand (John 13:28–29).

John's writing makes numerous references to the idea of "light" (John 1:4; 3:19; 8:12; 12:35; 1 John 1:7; 2:9; Revelation 22:5). This is used as a reference to the ideas of life, truth, God, and goodness. When John says that Judas went out into "night," it's much more than just a minor detail thrown in for no reason. Jesus has pointed out that the one who betrays Him is utterly lost (Mark 14:18–21). Judas' own choices have brought him to the point of being utterly controlled by Satan. The symbolism of Judas stepping out into the night reflects the abject destruction he's chosen for himself (Proverbs 29:1).