"One thing must be emphatically stated.

The New Testament books did not become authoritative for the Church because they were formally included in a canonical list; on the contrary, the Church included them in her canon because she already regarded them as divinely inspired, recognizing their innate worth and generally apostolic authority, direct or indirect. The first ecclesiastical councils to classify the canonical books were both held in North Africa-at Hippo Regius in 393 and at Carthage in 397-but what these councils did was not to impose something new upon the Christian communities but to codify what was already the general practice of those communities."

~FF Bruce, The Reliability of NT documents, Ch 3.