N.T. Wright on definitions

One of my favorite, and possibly my very favorite, theologian, in an interview, recently discussed the recent phenomenon of gay marriage.  He, being an Anglican, is in the middle of this discussion.  His critique and answer for this historical deviation was phenomenal.  You can read it here.  In summary, he argues that marriage has never been seen as anything but between a man and a woman.  To suddenly redefine it as anything else, simply because of cultural preference, is simply not honest.  Reality doesn't work that way.
I would like to take his approach and apply it to Christendom in general. The first 800 years of Christian history shows us the church's work of definition and articulation of faith and practice.  This time period saw the seven ecumenical councils and the way the church handled beliefs that differed from the historical and apostolic faith. But eventually, after decades and centuries of slight deviation (around 1050), the Roman church led by the Roman bishop, better known as the pope, decided that all other jurisdictions needed to submit to the pope as final authority.  The other jurisdictions responded with saying that the church had never lived out its that way.  That such a belief and practice would be an innovation.  This brought the first major division within Christendom.
About 500 years later, the Protestant reformation started, causing another massive split within the church.  

The common factor among these two events is that of definitions.  Christianity had been defined as the faith in Jesus Christ as handed down by the apostles and their successors.  Any change of definitions would not be honest.  Why would we think that redefining central trends or practices would even make any sense?  We all need to step back and look at how we define our faith and why.