In John's Gospel (especially chapter 15) the friends of Jesus are charged primarily with producing love. That is, his 'philoi' are expected to 'agapao' him. This puts a new slant on the Greek verbage of John 21. For that matter, if one were to classify the "loves" of classical Greek, 'phileo' (the faithful love of a friend) would rank higher than any other human experience the Greeks themselves had known.
Thus, Peter's response (philw se) to Jesus' question (agapas me) was hardly the anemic 2nd rate profession of so many sermons. Rather, Peter's response was affirmative to the highest degree. Furthermore, John's placement of this event at least twelve days after the resurrection, and his mention of Peter growing listless in Jerusalem, combine with this linguistic suggestion in order to cast a new light on this whole exchange.
Jesus' question (agapas me) is the obvious prelude to asking a favor. Peter's response (philw se) is a way of saying, "You know I'm your man." The clear implication is that Peter is eager for something to do. Jesus' challenge the third time suggested Peter might not really go through with that which was going to be asked of him. That's why it grieved Peter so. They weren't debating emotion. They were discussing the responsibilities of loyalty. That's also why the conversation ended up at the cross.
I've said this before. I just felt like saying it again.
If anyone wants to help me run due dilligence, and turn this into a publishable article, I'd love to collaborate. I'll also happily settle for a footnote. Just read the rest, please. (And this bit, about loving the fish.)