A.T. Robertson Commentary John 21:17

"He saith unto him the third time, Simon, [son] of John, lovest thou me? Peter was grieved because he said unto him the third time, Lovest thou me? And he said unto him, Lord, thou knowest all things; thou knowest that I love thee. Jesus saith unto him, Feed my sheep." — John 21:17 (ASV)

Lovest thou me? (φιλεις με; ). This time Jesus picks up the word φιλεω used by Peter and challenges that. These two words are often interchanged in the N.T., but here the distinction is preserved. Peter was cut to the heart (ελυπηθη, first aorist passive of λυπεω, to grieve) because Jesus challenges this very verb, and no doubt the third question vividly reminds him of the three denials in the early morning by the fire. He repeats his love for Jesus with the plea: "Thou knowest all things."

Feed my sheep (βοσκε τα προβατια). Many MSS. both here and in verse 16 read προβατα (sheep) instead of προβατια (little sheep or lambs).