If I then, the Lord and the Teacher, have washed your feet, you also ought to wash one another’s feet. For I have given you an example, that you should also do as I have done to you.
Everything about this scene is the wrong way round, and John wants us to feel it. Jesus is on His knees with a basin, washing the feet of men who call Him Teacher and Lord, one of whom would deny Him within hours and one of whom would betray Him that night.
That is the detail that makes this more than a lesson in kindness. He washed all twelve. He did not wait to see who deserved it, and He did not withhold the towel from the man He knew was about to sell Him.
He also gives the reason plainly. Not because it is a good idea, but because He has done it first. The pattern moves downward before it moves outward.
So the example is specific. It is not a general instruction to be pleasant. It is an invitation to do for someone else the small, unglamorous, slightly humbling thing that is actually in front of you.