If Jesus, who is really Lord and Master, has given them a humble service, then they should have no qualms about doing the same for each other. Jesus gave them an example, a living parable. Morris notes that, “It is unlikely that this is to be taken as a regulation promulgated in the interests of pedal cleanliness.” Jesus is showing them that they should not be hesitant to deliver the most menial of service to each other. There is nothing they could do for each other that is too low or humiliating for them to do. They were in need of this instruction (Matt 20:20-22, Mark 9:33-34, Luke 22:24). So are we.

Matthew 20:20-22  Then the mother of Zebedee’s sons came to Jesus with her sons and, kneeling down, asked a favour of him.  “What is it you want?” he asked. She said, “Grant that one of these two sons of mine may sit at your right and the other at your left in your kingdom.”  “You don’t know what you are asking,” Jesus said to them. “Can you drink the cup I am going to drink?” “We can,” they answered.

Mark 9:33-34  They came to Capernaum. When he was in the house, he asked them, “What were you arguing about on the road?”  But they kept quiet because on the way they had argued about who was the greatest.

Luke 22:24  Also a dispute arose among them as to which of them was considered to be greatest.