Neil (OSO) objected to my brief post on the VB where I said "it's an extremely marginal belief and not essential to faith". Well. Whilst I'm on the subject, let's dig in a bit more. Or: I may as well be hung for a sheep as a lamb! I think there are two broad grounds for saying the the VB is a marginal belief, the first is Scriptural, the second doctrinal. The Scriptural side is short and sweet, which means I can fire this one off immediately. The doctrinal one may have to wait until after Christmas (dependent on how my sermon preparation goes today...)
The VB is testified to in 2 places in Scripture, the prologues to Matthew and Luke. It is not mentioned in Paul, Mark or John or any of the other writings. As such - given that we can be confident that they both had copies of Mark's gospel in front of them - we can say that the account is a late development in Scriptural terms.
Yet the Scriptural point goes rather deeper than this. It's not simply that the story is only mentioned in late strata, it's that there is no 'echo' of the story at any other point. To bring this out, let's compare the Scriptural witness to the Virgin Birth with the Scriptural witness to the resurrection.
The resurrection is testified to throughout Scripture, from the earliest to the latest, and, more crucially, it is testified to implicitly as well as explicitly. The text might rightly be described as saturated with the resurrection. It is the precondition for there being testimony about Jesus at all. Any recognition of Christ as Lord is dependent upon the resurrection in that without it he is simply a criminal condemned to a shameful death, and bearing the curse from God that results. Without the resurrection there is no gospel.
The same cannot be said for the story of the Virgin Birth. It is not a precondition for communicating the gospel - or else Mark and (most especially) John would have needed to give an account of it. Paul would have made some mention or reference to it; given all the things that he DID talk about it would be odd if something so allegedly central were not referred to, particularly given his appeal to a gentile audience (after all, it's the sort of story that such an audience could expect to understand swiftly). Indeed there is at least an indication that Paul believes things in contradiction to the VB - consider Romans 1.3, when he says of Jesus that he was "as to his human nature a descendant of David" - how does that reconcile with Joseph not being involved in his paternity? There is no clear prophecy of it in the Old Testament either - despite Matthew's attempts to find one, again, in contrast to other features of Christ's life, death and resurrection.
One can ask - if the story is removed from the New Testament, how much damage would be caused? (For comparison: if the resurrection were removed from the NT, consider how much damage would be caused!) For we would not need to remove all the details of the two (different) birth accounts; we would merely need to remove the word 'virgin' and the sentences reinforcing it. Would anything else be removed at the same time? Well, all the accounts about Joseph can be left in place. All the language about Mary saying 'yes' to God can still be in place, and the Magnificat is untouched (hooray!). If, for example, we hypothesise either an illegitimate union between Mary and Joseph, or, perhaps, a rape of Mary or something like that - ie something which gives rise to some 'scandal' and which needs to be overcome by angelic support to both Mary and Joseph - then I don't see what of any substance is lost. We can still talk about God's being the prime mover in a situation, and there's no need to abandon any parallelism with the Genesis account of the spirit moving over the face of the waters.
To my mind, nothing is lost, and potentially a great deal is gained. But the gains can't be considered without going into the doctrine, ie what is at stake in this insistence that the story of the VB is true? That'll come later.