The Bare Necessities

I plan to begin an extended consideration of Matthew 16:13-19 soon, but before I do I want to continue to explore C.S. Lewis's analogy a bit (for those just tuning in, Lewis likens the church to a house with many rooms, each of which represents a particular denominational tradition. The rooms open up to a common hallway, which represents what he calls "mere Christianity").

Now, in a real house there is rarely any ambiguity about where the hallway actually is. I mean, it's pretty obvious, right? That long narrow thing with doors on either side? That's the hallway.

But is it that simple in Lewis's "house"? What exactly constitutes "mere Christianity" anyway? I know that D.L. Moody claimed he could write the gospel on a dime, but that just causes one to wonder if the message that can fit on it is worth more than the coin it's written on.

Is Reformed covenant theology a part of "mere Christianity"? What about the substitutionary atonement? Infant baptism? The real presence of Christ in the Supper? The ever-virginity of Mary?

My guess is that Clive Staples would tell us that "mere Christianity" is what you find in the creeds of the early church. The question immediately arises, "Which ones?" Do we accept the declarations of the first four councils (Nicaea, Constantinople, Ephesus, and Chalcedon)? The first seven? All twenty-one?

And if our answer is that we only accept the decrees of those councils that were faithful to Scripture, then does that not just put us back in the position of not agreeing about where the hallway is?

I guess what I'm asking is this: Ought our faith to be reduced to its lowest common denominator? And if not, how much unity are we willing to sacrifice for the luxury of expressing our faith more robustly?