[I am starting a series on Scripture which I will add to every few days for the next few weeks. It is my hope that these posts will generate some discussion, so if you're the sort of person who reads my blog but never comments, now is your chance...]
The question of the canon of the Old Testament is the first we must deal with. It seems to me that we can affirm that Jesus and the apostles would probably have considered all of the books in our canonised Old Testament as scripture. However, whether they would have considered other books besides these is open for debate, and whether they had much of a notion of canon at all is difficult to decide.
While it seems doubtful that there was a settled canon of the Old Testament during the time of Jesus it seems clear in the Gospels that Jesus accepted, without qualification, the existence of scripture. From his quotations and allusions to the Old Testament we can ascertain that he would have considered most (and so, probably all) of what we now call the Old Testament to be part of Scripture. It might be the case that Jesus accepted as scripture some books that were not added to the canon (some of the non-canonical portions of the LXX, for instance) but we have no direct evidence for this. He sometimes quoted scripture as the words of God and so clearly held to some notion of inspiration. So, it seems safe to say that what we now call the Old Testament is likely to have been accepted as inspired Scripture by Jesus himself.
When it comes to the attitudes of the apostles and early Christians it is again quite clear they held the same view. We have the clear evidence for Paul’s attitude — for example, in 2Tim 3:16: `Every scripture is inspired by God …’ — and we have an abundance of evidence throughout the Acts and the epistles in the way that the New Testament writers quote from and talk about Old Testament writings. Again, as with Jesus, the words of David, for instance, are sometimes referred to as the words of God and so there is again some notion of inspiration operating. The New Testament writers do, on occasion, refer to what would now be considered non-canonical writings and so there is some evidence that their canon might have been more inclusive than ours — perhaps comprising the entire LXX — but again this is difficult to say.
It is possible that the apostles and early believers, and perhaps Jesus himself, had no idea of `canon’ and may have seen scripture as something that could be added to. This is suggested by Peter’s willingness to consider the letters of Paul as scripture (cf. 2Pe 3:16).