I thought this was interesting. Like some other Fathers (though I don’t think all), Augustine makes a careful distinction between books received by the Church as being the very words of God, whose authority cannot be doubted in any respect, and books received by the Church as not having that status. Sometimes he uses the word “Scripture” for both, but he nevertheless retains a clear distinction between them. Those that are God’s words have “canonical authority,” while those that are not God’s words have no such authority.
We may, however, leave aside the stories contained in those Scriptures which are called ‘Apocrypha’ because their origin is hidden and was not clear to the fathers from whom the authority of the true Scriptures has come down to us by a most certain and known succession. There is, indeed, some truth to be found in these apocryphal Scriptures; but they have no canonical authority because of the many untruths which they contain. (City of God XV.23)
But it was not for nothing that even these were excluded from the canon of the Scriptures which was preserved in the temple of the Hebrew people by the diligence of the priestly succession. For the accuracy of these books was judged to be suspect by reason of their antiquity; and it was not possible to discover whether they were indeed what Enoch had written, for those who put them forward were not thought to have preserved them with due rigour through a clear succession.
Note in this connection that in the City of God Augustine often uses the phrase “the canonical Scriptures” when speaking of the undoubted words of God (e.g., XI.3; XV.23); also “Divine Book” (XV.23) and “Divine Scripture” (XV.7-8) “canonical books” (XVI.1). At XVII.24 he expressly equates “divine authority” with “canonical authority.”