Charles Ellicott Commentary John 13:7

"Jesus answered and said unto him, What I do thou knowest not now; but thou shalt understand hereafter." — John 13:7 (ASV)

What I do you do not know now.—Here both pronouns are emphatic and convey a rebuke to Peter. His words had almost implied that the Lord's act was wholly out of place, as of one who did not know what he was doing. The opposite was really the case. What I do you do not know now.

But you shall know hereafter.—That is, in the teaching which is to follow (John 13:13–17). The word rendered “hereafter” is different from that rendered “afterwards” in John 13:36. The precise meaning is “after these things.” The sense, then, is “What I do you do not know now; but you shall come to know presently.” (Compare John 13:17.)