What a great question, and I regret not having responded three months ago. Hopefully you will come back and see where I stand (and hopefully others will participate as well).

Your first assumption is correct - that I (I speak for myself; not for all EC's) belive the Rock is the knowledge of Christ (referred to time and time again as the Rock of our salvation, etc) as the Son of God.

The same knowledge is also the key to heaven. The Bible says no one can enter the kingdom of heaven unless they are born of the Spirit [of Christ]. Salvation is the key, and salvation only comes through faith in Christ Jesus as the Son of God....the whole of the church is based on salvation, when we come into the Body of believers. That is the one fundamental key that unites Christians as the Body (church).

I hope that made some sense.