Quick Reason:
After centuries of narrowing the list of books trusted to be
used in the Liturgy the Church formally agreed upon the list of books in the
New Testament at various councils attended by many bishops and approved by the
Bishop of Rome.
Long Reason:
Certainly, the current list of New Testament writings
neither fell from the sky with a bow and a message “From: God” nor were picked overnight by the
councils of the last fourth century. The
list of books in consideration had been narrowed considerably by generations of
use within the liturgy. However, as a
Church that spanned the known world, more than common consensus was
needed. By the lend of the fourth
century the Church was ready to make a decision.
The first council that appears to have the same list of New
Testament books as we have today is the Council of Rome in 382. A council in Hippo (North Africa) in 393 did
the same and this council was affirmed at two councils in Carthage (also North
Africa) in 397 and 419.
These councils didn’t close the canon; that didn’t technically
happen until the Council of Trent in 1546.
However, they solidified within the Church the writings of the New
Testament to be trusted as inspired. It
was no longer up to individual churches to maintain their own list; that era
had passed.
That the bishops and the pope confirmed the New Testament
books with certainty gives Catholics confidence in them.


