I’m fascinated by Plantinga’s account of mere Christianity as “the intersection of the great Christian creeds”. On this account, mere Christianity is fundamentally and overwhelmingly Incarnational and Trinitarian. This seems to me unavoidable even in the Apostles’s Creed, but at the very least there is a clear development in the Creeds towards an explicit Trinitarianism and traditional christology (i.e. Christ is two natures, remaining whole and diverse, united in one divine person.)
There seems to be something fundamentally right and even unavoidable about defining mere Christianity in this way, but it also seems to lead to a view of Christian argumentation and discourse that is very different from what is usually called “mere Christianity”.
1.) What we call “mere Christianity” seems more heavily weighted towards theistic proofs and the reality of sin. The Creeds, however,
mention none of don’t stress this. On this account, what we call mere Christianity should be called pre-Christianity. But what is this? Paganism? The Old Covenant? Rational ethics with a splash of “religion”?
2.) We tend to argue all properly Christian claims from the viewpoint of a theologian doing scriptural exegesis, i.e. from a guy who is either working from his own wits or from some one of the approved contemporary exegetical traditions. So where are the creeds? They seem to be nowhere to be found – or, what’s worse, they are taken as objects to be critiqued in light of exegesis. The creed is simply not taken as being regulative, or as expressing a mere Christian tradition within which exegesis must be guided.
3.) We might want mere Christianity to be Apostolic or dating to the time of the New Testament writers, but it is impossible to place it there. The Apostolic age gave us everything, and so could not give us the mere basis. By definition, “mere Christianity” suggests refinement, minimalization, precision of discernment, etc, which all presupposed a large mass that was given without any such activity being performed upon it. No, if mere Christianity has any hermeneutical value, then either it comes from the Christian tradition or it starts with us – though this latter opinion is hard to distinguish from the claim that the Christian tradition has no value at all.