John Gill

Jesus answered and said unto him,.... Christ replies, what I do, thou knowest not now: Peter knew that he was about to wash his feet, and the rest of his disciples, but he did not know the meaning and mystery of it, what Christ designed by it, and what instruction they were to receive from it, but thou shalt know hereafter; as he did, when he had performed this service, and explained it to him. This may teach us, under dark providences, the meaning of which is not yet known by us, to wait the Lord's own time, to make things clear and plain to us, and in the mean time patiently submit to the divine will.