When Jesus said that one of the disciples would betray Jesus, some of them became worried. Then Peter asked who is the one. Jesus told Peter that the betrayer is the one that Jesus gives the bread to (13:26). That person was Judas Iscariot.
After Judas got the bread, Satan (AKA the devil and ultimate villain) entered Judas (likely since Judas's heart was already focused on betraying Jesus anyway). But then Jesus made a peculiar comment -- he tells Judas that what Judas was planning to do, Judas should do quickly (13:28). Even the disciples don't know what Judas was planning to do at first! But eventually, we know that Judas ran out after taking the bread (13:30).
So what did Jesus intend when he told Judas to do what he was planning to do quickly? It's likely that Jesus knows that Judas would run out, so he would want Judas to do what he wants as soon as possible to avoid Judas from further interfering with the disciples. But it's also likely that Judas's betrayal would lead to the crucifixion of Jesus, which is part of Jesus's plan to take on sin and death on behalf of humanity.