The notion of "improvising" is important [...] improvisation does not at all mean a free-for-all [...] but [...] disciplined and careful listening to all the other voices around us, and a constant attention to the themes, rhythms, and harmonies of the complete performance so far, the performance which we are now called to continue. At the same time, of course, it invites us [...] to explore fresh expressions, provided they will ultimately lead to that ultimate resolution which appears in the New Testament as the goal, the full and complete new creation [...] anticipated in Jesus's resurrection. All Christians, all churches, are free to improvise their own variations designed to take the music forward. No Christian, no church, is free to play out of tune.Wright's analogy is interesting. I actually feel somewhat decent about it, and I really want it to be true. Of course, I also think that it's problematic; to give a brief example, let's say I'm composing a song. I start with a bass-line and then proceed to build other lines, lead-lines, chords, etc., over it. Eventually I run across two synth-lines, neither of which seems to conflict with the bass-line. But they conflict with each other. Do we (a) choose to believe that the song still sounds fine even with the dissonance (sometimes in music dissonance is called for), (b) identify one of those synth-lines as being more out of tune with the previously established music, or (c) come to the conclusion that them being out of tune means that they both need to adjust?
Perhaps most importantly: What's the bass-line? For Wright it appears to be Scripture primarily, followed by history and reason. But not all Christian churches necessarily agree with that. I think Wright's analogy is definitely onto something, at least in terms of finding what unity of action we currently have. But I think it becomes incomplete when we reach scenarios like the one above, where different churches' music seems equally compatible with the past, but incompatible with each other. Wright does offer in the next few pages his own solution for attempting to read the Biblical text so as to make sure that we're all 'in tune with the bass-line,' to use my example. But there will still be things left open to interpretation. For example, the debate over the relation of providence to free will continues to be an issue even when Wright's criteria are met. But again, I think Wright's onto something, especially when he adds his criteria for respecting Scripture's authority.
N.T. Wright, The Last Word (USA: HarperOne, 2005), 126-127. For further discussion on how to make sure your improvisations are in tune, pages 127-142, essentially the last part of the book, offers Wright's recommendations. If you want a more contextualized and less for-this-week reading of Wright's comments on unity, I highly suggest reading The Last Word. If nothing else it is worth reading for the hilarious lists of misreadings of the "left" and "right" on pages 106-110.