John Gill

If I then your Lord and Master,.... Christ argues from these titles and characters, which his disciples rightly gave him, and from what he had done to them, though he stood in such a superior relation to them, to their duty one towards another; that since, says he, I have washed your feet, ye also ought to wash one another's feet: by which he does not mean barely, that they should perform this single action; but as this was an instance of humility and condescension, and doing a good office to strangers and travellers, and was afterwards an expression of love to the saints, see Ti1 5:10, so he would teach them hereby, to behave in a spirit of humility and condescension to one another, to do every kind and good office, and by love to serve one another in all things.