What does it mean that something is extrabiblical / extra-biblical?

Now, what is it that really makes a group of Christians a sect, or sectarian? Mainly two things. One is to formally create an organisation to which you need to belong before you can enjoy fellowship with the other ‘members’. The other is to impose conditions on those who are received into fellowship – not the biblical conditions of pure walk, doctrine and association – but extra-biblical requirements, e.g. a certain dress code.

In 1868 the German missionary Klein found a stone in Dibon (a town in Moab, East-Jordan land) with the inscription of Mesa, king of Moabites (compare 2 Kings 3). On this stone Mesa recorded in ancient Hebrew letters his disputes with King Jehoram of Israel. This stone dating to the time 840 BC is probably the most ancient extra biblical written testimony for the absolute correctitude of the Old Testament accounts on historical facts. (This stone can now be seen in the Louvre, Paris.)

Yes. Any third party's testimony would be rather weak. If God has revealed Himself (as every Christian believes He has) in His word, then His word will speak about and for itself. Extra - biblical evidence would only detract from its inherent authority. The only place where we can learn whether the Bible is inspired, and what exactly this means, is: in the Bible! God's book speaks for itself.

Great respect has constantly been shewn to the so-called fathers of the church, and to their writings, especially to the apostolic fathers. Naturally we might think that those who had the privilege of intercourse with the apostles would themselves be well instructed in the truth. But we doubt not that God allowed that there should be a deep, dark line of distinction between writings that were inspired and those that were not. And this we find to be the case, so that no one should be mistaken as to which is scripture and which is not. This difference is gathered from internal evidence, too plain to be mistaken; for indeed, external evidence might otherwise have led us astray, seeing that in the ancient Greek manuscripts some of these writings were placed along with the inspired books, and were in early days read in the meetings of Christians.*

Now there were in existence certain writings, known upon particular and specific evidence to have been written by men used of God to do so. By far the greater proportion of these writings are addressed to persons (often to assemblies of persons) with whom the writer was acquainted. No great number of books were ever promiscuously, and as having equal claims, submitted to the judgment of men, but certain particular writings possessed peculiar and notorious claims, from the time they were received — claims which were never detached from them. The evidence for their genuineness (I allude here to the outward evidence, which itself is logically decisive; but there is likewise an inward evidence of the divine origin of Holy Scripture, which is no less, nay, even more, decisive to those who, through the grace of God, are acquainted with it) was unofficial, but reliable human — i.e. personal — testimony, originated and maintained by divine Providence; and so clear and conclusive, that, with extremely few exceptions, to know that such writings existed was almost to know which they were, since the sacred writings created their own fame, as do all the works of God. (Psalm 145:10). As to the few exceptions, the same principle was involved of letting God's Word speak for itself, i.e., letting the claims of what really was God's Word be heard alone; whereas whatever difficulties there were, were produced by the folly and wickedness of men in regard to their own writings (the Apocrypha for instance — the apostolical constitutions, besides a swarm of evidently spurious gospels), which the Church encouraged and availed herself of, but which was permitted by God to a limited extent only, though quite far enough to manifest the unfaithfulness of the Church. The settling the Canon of Scripture was, on the part of the Church, simply an official and formal recognition of already established evidence, not the discovery, still less the creation, of evidence. The Holy Scriptures were written by inspiration, they were identified (so far as man had to do with it) by ordinary but adequate human testimony.

1917 259 The word "tradition" occurs in scripture both in a good sense and in a bad sense. Broadly, the usage Of the term is with reference to religious instruction passed from one to another. The root idea is of something delivered to men. If the instruction is derived from God, the tradition is obviously of supreme and undeniable authority; but if derived from a purely human source, its authority is questionable, and its truth requires to be substantiated, before it can claim our acceptance.

At this time we meet with the expression 'ecclesiastical books.' It was applied to those books which, though regarded as not inspired, were considered worthy of perusal: they did in fact contribute to the Church lectionaries. The ancient MSS. of the LXX, as we have said, are evidence of the practice (cf. chap. 4 § 3). To this class appear to have been consigned the books of the LXX called in the Talmud 'extraneous' (ibid. 2).

By 'apocryphal,' as far back as we have been able to trace the word, and down to the fourth century, were meant such books as had grown up since the Alexandrian Bible was completed. The reader may consult Sophocles' Lexicon of Roman and Byzantine Greek, under ἀπόκρυφος (apokruphos), where references are given to Irenaeus, Clement of Alexandria, and Origen. We shall have to return to the discussion of its meaning when speaking of Jerome.

The Alexandrian collection took in more Books than the Hebrew: this may be seen from the Septuagint in its complete form. The accretions called 'external,' 'extraneous' in the Talmud, are to us known by the name of Apocrypha, meaning either, books with a hidden, mystical meaning, or, books that are kept back, though not lightly esteemed.* In modern Greek, the meanings of apokruphos seem to be secret, hidden, occult. We might perhaps compare the relation between these writings and those of our Old Testament to that between the Patristic and the New Testament writings.

Every kind. One positive reason is, that it never was in Hebrew at all; and as to outward testimony, it never was classed with the Scriptures by the Jews. But to have the real knowledge of the Scripture authority, you must have divine teaching. The division the Jews made of the Scriptures, was into, the law, the prophets, and the psalms. Josephus tells us there were prophets after the time of Artaxerxes (i.e., Malachi's time), but they were not of the same authority as those who went before. That, of course, is not a divine way of knowing about it. It is said that the Song of Sirach was translated into Hebrew, but it was not. The best way to determine about such books is to look into them. Take Maccabees, and you will find something to this effect: "I have done my best to make an epitome of the five books of such a man, for it is very tedious to have too much to read, and if I have done it well, then it is worthy of the matter," and so on. Think of saying that is inspired!