“Jesus answered him, “What I am doing you do not understand now, but afterward you will understand.” Peter said to him, “You shall never wash my feet.” Jesus answered him, “If I do not wash you, you have no share with me.” Simon Peter said to him, “Lord, not my feet only but also my hands and my head!” Jesus said to him, “The one who has bathed does not need to wash, except for his feet, but is completely clean. And you are clean, but not every one of you.” (John 13:7-10)
Peter’s horrified reaction at Jesus’ washing of his feet is the reaction of normal human nature. That the disciple should wash his master’s feet is normal and proper. But if the master becomes a menial slave to the disciple, then all proper order is overturned…. All of us except those at the very bottom have a vested interest in keeping it so, for as long as we duly submit to those above us we are free to bear down on those below us. The action of Jesus subverts this order and threatens to destabilize all society. Peter’s protest is the protest of normal human nature.
… This is not just an acted lesson in humility; Peter could have understood that…. The foot washing is a sign of that ultimate subversion of all human power and authority which took place when Jesus was crucified by the decision of the “powers” that rule this present age. In that act the wisdom of this world was shown to be folly, and the “powers” of this world were disarmed (Col 2:15). But “flesh and blood” — ordinary human nature — is in principle incapable of understanding this. It is “to the Jew a scandal, to the Greek folly.” Only those whom the risen Christ will call and to whom the Holy Spirit will be given will know that this folly is the wisdom of God, and this weakness is the power of God. At that moment, as the man he is, Peter cannot understand. The natural man makes gods in his own image…. How can the natural man recognize the supreme God in the stooping figure of a slave, clad only with a loincloth?
~Lesslie Newbigin in The Light Has Come: An Exposition of the Fourth Gospel