For the first hundred years, at least, of it’s history the Church’s Scriptures, in the precise sense of the word, consisted exclusively of the Old Testament. The books comprising what later become known as the New Testament were of course, already in existence; practically all of them had been written well before the first century ended, and they were familiar to and used by second century writers. They had not yet been elevated, however, to the special status of canonical Scriptures…
It should be observed that the Old Testament thus admitted as authoritative in the Church was somewhat bulkier and more comprehensive than the … books of the Hebrew Bible of Palestinian Judaism. … It always included, though with varying degrees of recognition, the so-called Apocrypha, or deutero-canonical books. The reason for this is that the Old Testament which passed in the first instance into the hand of Christians was … the Greek translation known as the Septuagint… most of the Scriptural quotations found in the New Testament are based upon it rather than the Hebrew…
In the first two centuries at any rate the Church seems to have accepted all, or most of, these additional books as inspired and to have treated them without question as Scripture. Quotations from Wisdom, for example, occur in 1 Clement and Barnabas, and from 2 (4) Esdras and Ecclessiasticus in the latter. Polycarp cites Tobit, and the Didache Ecclesiasticus. Irenaeus refers to Wisdom, the History of Susannah, Bel and the Dragon and Baruch. The use made of the Apocrypha by Tertullian, Hippolytus, Cyprian and Clement of Alexandria is too frequent for detailed references to be necessary. Towards the close of the second century, when as a result of controversy with the Jews it became known that [the Jews] were united in repudiating the deutero-canonical books, hesitations began to creep in…
For the great majority, however, the deutero-canonical writings ranked as Scripture in the fullest sense… The same inclusive attitude … was authoritatively displayed at the Synods of Hippo and Carthage in 393 and 397 respectively, and also in the famous letter which Pope Innocent I dispatched to Exuperious, Bishop fo Toulouse, in 405.