Summary: Jesus had to deal with disappointing disciples. So do we. How do we deal with them? By applying the new Law of Love.
John 13 (quickview)  begins with the wonderful statement: ’Having loved his own who were in the world, [Jesus] now showed them the full extent of his love.’ It’s a picture of an intimate relationship with his disciples, like that of a loving parent who will do anything for their children. Yet even as he’s saying it, a shadow hangs over the scene. As he begins to wash their feet we discover their ignorance of his purpose. As he begins to explain what he’s doing he reveals what only one other of them knows: that one of this intimate group of disciples is a traitor.
In v10 he says: (John 13:10 (quickview)  NRSV) "You are clean, though not all of you." Then in v18 he says "I am not speaking of all of you; I know whom I have chosen. But it is to fulfill the scripture, ’The one who ate my bread has lifted his heel against me.’ 19I tell you this now, before it occurs, so that when it does occur, you may believe that I am he." It’s important for the disciples and for us to realise that even in this event, where one of those that he’s chosen will betray him, Jesus is still Lord. He isn’t taken unawares. Despite what popular culture might suggest, through such avenues as Jesus Christ Superstar, Jesus isn’t disillusioned when this betrayal occurs. He’s disappointed, certainly. Look at v21. "After saying this Jesus was troubled in spirit, and declared, "Very truly, I tell you, one of you will betray me." He’s emotionally affected by the thought that Judas would betray him. The image of a person lifting their heel against another is a reference to the way a horse or a donkey might kick you when you’re not looking. It’s something that’s vicious and done with cunning. And for one of his close friends, one who’s shared bread with him, to do that hurts even more.
But he isn’t taken by surprise by it or outwitted by it. In fact he tells them before it happens so that they’ll know with even more certainty that he is the one: "that you may believe that I am he." That is, that Jesus is the promised Messiah, the Son of God.
But that leads him to the next statement, in v20: "Very truly, I tell you, whoever receives one whom I send receives me; and whoever receives me receives him who sent me." It seems to me there are 2 sides to that statement. First of all it’s a comment about Judas. He’s saying, if Judas refuses to accept Jesus, the one sent by God, he’s therefore also refusing to accept God the Father. You get the feeling that even at this late stage, Jesus is trying to warn Judas of just how dangerous his intention is. His action of dipping the bread in the dish and passing it to Judas seems to be one final attempt to win him over. But it’s not to be.
But the second implication of Jesus’ statement is that if Jesus truly is the Messiah, then the disciples have an important task before them. It won’t be long before they’ll be sent out to preach the gospel and when that happens they need to know that the authority with which they go is the same authority with which Jesus preached. That is, with the authority of God himself. Not that that will automatically guarantee a warm reception mind you. In fact he tells them elsewhere that they can expect the same sort of treatment he received. But even so, they can take heart from the fact that when they go out to preach the gospel it’ll be as Jesus representatives, his ambassadors. So when they’re welcomed by their hearers, it’s as though their hearers are welcoming Jesus himself.