Quote from : The Writings of the New Testament: An Interpretation Book

On the other hand, inspiration - a criterion for canonization we might expect to play a great role - is not a factor. The Shepherd of Hermas and many writings either claimed inspiration or had it claimed for them, yet were neither universally nor ultimately accepted as canonical. In contrast, no NT writing claims inspiration for itself. The statement in 2 Tim. 3:16 that all Scripture is inspired by God (theopneustos) refers to Torah. Second Peter 3:16 refers to Paul's letters as though they were Scripture but does not say they were 'inspired.' In Revelation, 'inspiration' is certainly implied but not explicitly claimed. No doubt there was an increasingly widespread conviction that the NT writings were divinely inspired, but that notion did not appear to factor in as a criterion for canonization.