When Jesus washes his disciples’ feet, he is preforming a parabolic act. As with parables, we need to understand the context in order to understand what Jesus was trying to teach through the washing of his disciples’ feet.
It is well-known that hospitality in the ancient world included foot-washing. Since virtually all travel was by foot, a visitor should be allowed to “refresh themselves” when they arrive by washing their feet. If the host had servants, the task of washing the guest’s feet fell to the lowliest servant. For a Jewish family, the task would be assigned to a Gentile slave (Köstenberger, John, 405). In this case, Jesus takes off his outer clothes and wraps himself in a long towel and does the job of the lowliest slave.
Since this is a Passover meal, it is likely that each of the disciples have washed their hands ceremonially before touching the food of the meal. My guess is that the feet would need to be washed since the are most likely to have come into contact with uncleanliness, the slave who washed the feet would therefore himself be unclean.
This is therefore a shocking act by a Jewish teacher prior to the Passover meal. Jesus’ humble service of his disciples is an illustration of how the disciples are to continue his work after the resurrection.
Said R. Joshua b. Levi, “All acts of labor that a slave performs for his master, a disciple of a sage performs for his master, except for removing his shoe.” b. Ketub. 96a (Neusner, b. Ketub. 11:1, I.2.A; 9:440)
Jesus is due the titles Teacher (Rabbi) and Lord. Even if we take the title Lord as equivalent to sir, both titles put Jesus well above the disciples socially. In a teacher-student relationship of the Second Temple Period, there was little a teacher could not ask his disciple to do for him. Yet Jesus reverses cultural expectations by doing an extremely humbling service for his disciples.
This is a pattern for the disciples to follow (v.15). The noun used here (ὑπόδειγμα) has the sense of a pattern, or model used for moral instruction. Jesus is saying this is an illustration of how you are to serve one another. This is not a pattern to be followed for worship, for example. Although there is nothing particularly wrong with practicing foot-washing in some Christian denominations, it is not an ordinance like the Lord’s Supper. To me this is analogous to saying the Lord’s Prayer. It is not particularly wrong, but misses Jesus point when he gave the prayer of an illustration of how to pray!
How do we serve as Jesus did? First, Jesus did not insist on his titles and honors. Ideally, Peter ought to have served Jesus, but Jesus radically reverses expectations and serves those who are socially lower than himself. If the Lord (and God) of the universe can get down on his hands and knees to wash the feet of those who owe him honor and loyalty, how ought we to serve?
Second, notice that he washes all the disciples’ feet, including Judas. He knew that Judas was the betrayer, yet he extended to him the same humble service that he gave the other “loyal” disciples. Jesus knew that Satan was about to enter Judas and he knew exactly what Judas was about to do, but he treated him in exactly the same way he did Peter or John. That is remarkable to me. I have no problem humbly serving my family or my church family. But what about those who are outside the church? There are people who are outside of my normal circle who I do not serve, in fact, I sometimes treat them with contempt.
Jesus did not, he died for them as well.