Here is a two-part post by Mark Dever that is well worth reading.
He looks at the essentials of Christianity--those basics we must agree upon. He gives three ways that we learn what we must agree upon, gives a fourfold test you can put on a doctrine to discern its importance, and then gives three things ("the essentials of the essentials") that we must agree upon to have meaningful cooperation as Christians.
Part 1, Part 2.
