Thank you everyone for your stimulating replies. You have all made me stop and think. At the moment I have a jumble of isolated thoughts going through my mind but I don’t seem able to integrate them and move forwards. So any further feedback would be appreciated!

Did Jesus endorse the idea of fixed canon of Scripture? Did he sharply differentiate between, say, the book of Deuteronomy and the Book of Jashar (mentioned in Joshua 10:13)? … and between the book of Kings and the Annals of Solomon (mentioned in 1 Kings 11:41)? … and the scroll of Isaiah and the prophecies of Enoch (mentioned in Jude 1:14-15)? Did he regard some writings as divinely-inspired and authoritative while other religious books were simply useful and edifying?

From the Gospels I get the feeling that he did have a concept of a rigid canon that distinguished the written Word of God from other edifying literature. In John 10:35 Jesus said that Scripture cannot be broken, and in Luke 24:44 he said “Everything written about me in the Law of Moses and the Prophets and the Psalms must be fulfilled.” I don’t know the exact list of books that Jesus included in Scripture, but I think he did have a sharp dividing line between those books that were in and those that were out.

However, I have read that the Jews did not officially define their canon of Scripture until the end of the 1st century AD, several decades after Jesus walked the earth.

In contrast to Evangelical Christianity, Jesus and his contemporaries were very free and easy about quoting Scripture imprecisely. Some of their quotations do not match exactly with any known Old Testament manuscript, either Hebrew or Septuagint. It seems they were content to give the gist of the original text rather than the exact words. In John 7:38 Jesus quoted something from the Old Testament so imprecisely that no-one is sure where he was quoting from. And in 2 Corinthians 6:16-18 Paul conflates several Old Testament texts to bring out a nuance that is not present in any one of the component texts.

Did God intend to create a New Testament with an equally rigid canon? Or is the New Testament merely a collection of writings that the early church found most relevant but which should not be greatly elevated above books that narrowly missed the cut, such as the Shepherd of Hermas and the Epistle of Barnabas?

I get the feeling that the early church did come to regard the New Testament canon as consisting of books that were uniquely divinely-inspired and in harmony with each. The following is a quotation from Justin Martyr’s “Dialogue with Trypho”, chapter 65. It was written sometime between 139 and 161 AD.
“If you spoke these words, Trypho, and then kept silence in simplicity and with no ill intent, neither repeating what goes before nor adding what comes after, you must be forgiven; but if[you have done so] because you imagined that you could throw doubt on the passage, in order that I might say the Scriptures contradicted each other, you have erred. But I shall not venture to suppose or to say such a thing; and if a Scripture which appears to be of such a kind be brought forward, and if there be a pretext[for saying] that it is contrary[to some other], since I am entirely convinced that no Scripture contradicts another, I shall admit rather that I do not understand what is recorded, and shall strive to persuade those who imagine that the Scriptures are contradictory, to be rather of the same opinion as myself.”

However, tempering this ‘Evangelical’ viewpoint, it seems that some scribes in the early church had no qualms about doctoring the New Testament text to suit their own prejudices. Some of the variants in Bible texts appear to have arisen due to deliberate changes by copyists with sincere religious motives. So they did not seem to regard the text as the sacred and inerrant written Word of God.

Muslim apologists are keen to point out textual discrepancies between parallel passages in different manuscripts, and they attack the Bible as being so corrupted as to be unreliable. I once put this problem to several ex-Muslims who had converted to Christianity from an Arab/Middle East culture. The gist of their reply was that any imprecision in the text is not important because we don’t worship a book but rather we worship the living Word, who is Jesus Christ, and that our relationship with him is not restricted by errors in the Biblical text. (Although they were talking primarily about textual corruptions, I suppose you could extend their answer to cope with the possibility of an erroneous canon.)

I would agree with what they say, but where does that leave Christians today who are looking for definite answers to ethical questions such as abortion, homosexuality, divorce & remarriage, and pacifism? The answers to those ethical questions may change if you start treating some of the extra-canonical books as equally authoritative as the canonical books, so surely we do need to have a clearly-defined canon if we are to determine God’s will for our lives.