A few years ago I stopped by a field of sunflowers to take some pictures, and filled a CF card with some fairly predictable, cliched pics of big gaudy yellow things that look like daisies on steroids. The best things are usually not the ones we were looking for, so, even after fiddling with them in Photoshop, I wasn't really pleased with any of the sunflower shots except this one; :
which the more observant amongst you will have spotted is probably not a sunflower. The colour's wrong somehow. The shape is odd. So what do you call it? A thistle? A nodding thistle? A musk thistle? Carduus nutans? A weed? A noxious plant? A reminder of the Highlands? A thing of beauty? A nasty nest of prickles? Now you need to be careful with your answer because what you call something doesn't define the thing named. It defines you.
The little ball of purple spines is completely unaffected by the name I give it - it lives on, soaking up sunshine, seducing bees, photosynthesising, nodding. The name I chose to give it states my relationship to the plant, my education and history, my emotional and affectional states with regard to it. In the same way, the names people give me - Kelvin, son, Vicar, Kel, sir, Dad, Reverend, IRD #465399, Sweetheart, you prat, Next! Yes you - define them, not me. That is of course, unless I make the mistake of taking the name to heart and using it to name myself, in which case I allow myself to be defined by some other's idea of who and what I am.
Which is the point of Jesus' question to Peter in Matthew 16, who do you say that I am? I notice that although Jesus doesn't refute Peter's insight, Why you are the Christ! he doesn't pick it up and use it himself and he was fairly insistent that people not go telling others their opinions of who he, Jesus, was. The conversation delivered Peter to a place he didn't even know he was traveling to - a new sense of Jesus and a new sense of himself.
Jesus is who he is; what Peter calls him defines Peter. What we call Jesus defines us.