John 21:17

(Hom. lxxxviii) A third time He asks the same question, and gives the same command; to show of what importance He esteems the superintendence of His own sheep, and how He regards it as the greatest proof of love to Him. (Hom. lxxxviii) The question asked for the third time disturbed him: Peter was grieved because He said unto him the third time, Lovest thou Me? He was afraid perhaps of receiving a reproof again for professing to love more than he did. So he appeals to Christ Himself: And he said unto Him, Lord, Thou knowest all things, i. e. the secrets of the heart, present and to come.

(de Verb. Dom. serm. 50) He was grieved because he was asked so often by Him Who knew what He asked, and gave the answer. He replies therefore from his inmost heart; Thou knowest that I love Thee. (Tract. cxxiv) He says no more, He only replies what he knew himself; he knew he loved Him; whether any else loved Him he could not tell, as he could not see into another's heart: (non occ.). Jesus saith unto him, Feed My sheep; as if to say, Be it the office of love to feed the Lord's flock, as it was the resolution of fear to deny the Shepherd.

To feed the sheep is to support the believers in Christ from falling from the faith, to provide earthly sustenance for those under us, to preach and exemplify withal our preaching by our lives, to resist adversaries, to correct wanderers.

There are indeed many other things which are able to give us boldness towards God, and to show us bright and approved, but that which most of all brings good will from on high, is tender care for our neighbor. Which therefore Christ requireth of Peter.

When then having been asked once and again, he called Him to witness who knoweth the secrets of the heart, and then was asked even a third time, he was troubled, fearing a repetition of what had happened before, (for then, having been strong in assertion, he was afterwards convicted,) and therefore he again betaketh himself to Him. For the saying, "Thou knowest all things," meaneth, "things present, and things to come." Seest thou how he had become better and more sober, being no more self-willed, or contradicting? For on this account he was troubled, "lest perchance I think that I love, and love not, as before when I thought and affirmed much, yet I was convicted at last." But Jesus asketh him the third time, and the third time giveth him the same injunction, to show at what a price He setteth the care of His own sheep, and that this especially is a sign of love towards Him.