[kosta50]

Because the Church fathers told us. ;O)

Cute. And the Apostles quote overwhelmingly from Septuagint (LXX) which the Protestants reject. And the Church Fathers used deuterocanonical books, which the Protestants also reject. The Protestants seem to recognize only that which they want tom hear, and read their own canon.

[HarleyD]

And the Apostles quote overwhelmingly from Septuagint (LXX) which the Protestants reject.

I wouldn't say "overwhelmingly". I believe there is only one or two instances. This hardly means they approved of ALL the books or ALL the writings in each book. For example, Paul states:
Tts 1:12 One of themselves, [even] a prophet of their own, said, The Cretians [are] alway liars, evil beasts, slow bellies.

I sincerely doubt that the Orthodox or Catholic Church view pagan prophets as inspired writings even though Paul quotes from them. Nor do I believe, or hope, their writings appear in the Septuagint. The writings may contain some true but those truth are true only as far as they are in the inspired writings.

BTW-This is an excellent example where "all" does not always mean "all". Obvious Paul is generalizing when he say all Cretians are "liars" as he salutes the Cretian bishops in Titus 3:15. Clearly he does not believe the Cretian bishop to be a liar.

And the Church Fathers used deuterocanonical books, which the Protestants also reject.

Which list are you speaking from? They all had different ones you know.