What does John 13:21 mean?
Earlier in this chapter, Jesus commented about the difference between someone who was "bathed," and needed only minor washing, versus those who were unclean (John 13:10–12). He hinted that not all of those present were clean—an allusion to Judas, who has already planned to betray Jesus (Matthew 26:14–16). That impending treachery was also mentioned in reference to Psalm 41:9 and the idea of someone sharing bread, but being traitorous (John 13:18). Jesus mentioned this so that the remaining disciples would not lose all hope when they saw what was to come (John 13:19). Here, Jesus makes that prediction explicit.Jesus is described using similar terms to His reaction at the tomb of Lazarus (John 11:33). The Greek root word translated as troubled in the ESV refers to something turbulent and disturbed. Speaking of what is about to happen causes Jesus emotional pain. Not only is Judas choosing treachery, he's opting for damnation (Mark 14:18–21). That's heartbreaking on many levels. Speaking these words also brings Jesus' human nature face-to-face with all the pain and misery about to come His way.
John 13:21–30 describes Jesus' awareness that Judas is a false believer. Rather than outing Judas as a traitor, Jesus simply mentions that one of the group will betray Him. That blunt statement confuses the disciples, who look at each other with suspicion. Jesus subtly identifies Judas in a comment made to John. This goes unrecognized until much later. Judas, however, knows exactly what the gesture means. At that moment, he is entirely under the control of Satan, and Jesus tells him to leave. The disciples assume Judas has been sent on a private errand.
Jesus meets with a smaller group, possibly only the twelve disciples, in a private setting. Before eating a meal, Jesus performs the work of a lowly servant, washing the feet of the disciples. He explains that this is an object lesson. Their Lord is willing to serve in humility, so they are obligated to do the same. Jesus also predicts His impending betrayal, subtly telling Judas to leave and complete His conspiracy. The disciples don't realize what's happened, however. Peter foolishly brags about his loyalty. Jesus responds with a cutting prediction: Peter will deny his relationship to Christ three times in the next few hours.
