Essentially, Orthodox dilaiect not withstanding, I think ironsiderodgers has explainied by and large the core esscence of what the NT church means to an Evangelical.
Also, it is used as point of reference -- the NT church deals with the existence of the church from the time of Christ through the time of the Apostles themselves, which is essentially conveyed in the the books of the NT canon, both in content and in time span. It deals with the primitive age of the church, it's beginnings.
As alluded to already, for us, that refers then to it's most pure state of existence yet. hence we seek to understand, immitate, and conform ourselves with it both in belief, polity, and practice.