If I remember correctly, the only books of the NT that were never in question were..
The four Gospels.
Acts.
All the letters of PAUL except HEBREWS.
1 PETER
1 JOHN
and that was IT.
The other books that were considered “doubtful” and not recognized for years...
That would be..
HEBREWS(one of my favorites, Uncertain authorship).
JAMES (too much difference from Paul’s letters)
2 PETER (Too different from 1 Peter in style of writing)
2&3 JOHN (Private correspondence, not inspired)
JUDE (Mentions verses from the book of Enoch)
REVELATION.(Too strange, too different in style from John’s other writings.)
It took several centuries before these were added to the bible.
And that is why the holy spirit guided the church into putting together the OT and NT, and only when questions arose, were the officially finalized.
that is why authority is entrusted to one body, one church, so you who use the bible, actually have one to use...
“It took several centuries before these were added to the bible.”
While your facts are more-or-less correct, your conclusion is false. You’re assuming the Church had a book called “the bible” which the later books were added to. NO.
Churches had collections of Apostolic books...and a few bishops and scholars did question your 2nd list, when finally in the 2nd and 3rd Centuries a FORMAL list of the Canon was put together.
Given their use, in quotations by the ante-Nicene Fathers, your latter list was actually accepted by the great majority of the Church....all along. When the list of Apostolic books was formalized did a few object—yes, but only because they were being extra careful.
Do doctrines taught in:HEBREWS,JAMES,2 PETER, 2&3 JOHN,JUDE & REVELATION alter or differ from the core list of NT books on the nature of Jesus or the gospel?
NO.
Did the church Fathers thouroghly examine the claims of Apostolic connection/or authorship in each of the books in question?
YES.
Therefore, is the New Testament as we have it now, the only reliable source of Apostolic teaching?
Yes.
I believe Mike Kruger’s main point here is that you trust the testimony of the Apostles, you must trust the New Testament—as that is the only record of it. Trusting the Apostles without qualification and trusting the Bible without qualification amount to the same thing.