Jesus washes the feet of his disciples; he humbles himself to them to show them how they must serve each other.
'Jesus, come, my feet are dirty. You have become a servant for my sake, so fill your basin with water; come wash my feet. I know that I am bold in saying this, bur your own words have made me fearful: "If I do not wash your feet you will have no companionship with me." Wash my feet, then, so the I may be your companion. But what am I saying, "Wash my feet"? Peter could say these words, for all that he needed washing were his feet. For the rest, he was completely clean. I must be made clean with that other washing, of which you said, "I have a baptism with which you must be baptised."' (Origen)
(from Bible Alive)