There are only two charcoal fires (Greek: anthrakia) mentioned in the whole Bible, and they are both in the Gospel of John. The first anthrakia mentioned was in the high priest’s courtyard, where the gatekeeper said to Peter, “You are not one of this man’s disciples are you?” and Peter says, “I am not.” Questioned like that two more times, Peter, now warming himself at the same fire, DENIES being a disciple of Jesus two more times (c.f. Jn 18:18, 25-27).
The second anthrakia mentioned was on the shore of the Sea of Galilee, apparently prepared by the Risen Christ (Jn 21:9). Here, the very same Peter was questioned; “Do you love me?” and the disciple now affirms his ALLEGIANCE three times.
So one anthrakia sets the threefold denial of discipleship, while the other anthrakia sets the threefold affirmation of discipleship. Coincidence? Knowing John’s Gospel, such symbology is likely not by chance. And who is to say that the association does not go back to Jesus himself, helping Peter to realize that the denier is being given a fresh start in his relationship to the Lord. This beach scenario is not only a matter of astounding forgiveness; it is also of commissioning: “Feed my lambs; feed my sheep.”
I’ve once asked a bunch of friends before – “Why did Jesus mention feeding his Lambs and then his Sheep? Like, what’s the difference?” This verse is deeply theological and the Church has the best answer: Jesus is commissioning Peter here to become not just leader of the laity (lambs); but also leader of the clergymen (sheep); symbolized through the young and mature in the flock.
Peter is given an opportunity to demonstrate the love he professed by sharing in the mission of the risen Lord. Ultimately, it is going to be a matter of being led where he does not want to go. Loving the head shepherd means obeying his commandments – even if it means becoming the first Pope, which would ultimately lead to his martyrdom.