Theophylact of Ohrid

For through the washing, which is considered the lowest service, He teaches that we should all the more fulfill the other services, which are more honorable. "I have given you an example, that you should do as I have done to you," that is, serve with the same zeal. Although My deed is greater, inasmuch as I, the Master, washed the feet of servants, while you would wash the feet of your fellow servants. Thus we see that teachers too write very beautiful letters for children, so that they may little by little come to imitate them. …

Commentary on John ↗

Thomas Aquinas

He supports his conclusion in four ways: first, by his intention; secondly, by his authority (v 16); thirdly, by the reward due this action (v 17); and fourthly, by the dignity of those whose feet he washed (v 20). He said the reason I did this was to give you an example; so you also ought to wash one another's feet, because that was what I intended by this action. For when we are dealing with the conduct of people, example has more influence than words. …

Commentary on John ↗

Bonaventure

I have given you an example, that as I have done to you, so you also should do: Matthew eleven: "Learn from me, for I am meek and humble of heart." And that he is to be imitated in works of humility, he shows by this reasoning: because the servant is not greater than his lord; therefore if the lord does not disdain to be humbled, much less should the servant. Question. It is asked here why the Lord gave his disciples an example of humility rather than of some other virtue, since there are other excellent virtues. …

Commentary on John, Chapter 13 ↗