[annalex]

The quotes from the Fathers serve two purposes: to show that the Catholic/Orthodox Church is the historical Christian Church and to elaborate the point.

I generally don't quote as much from the Old Testament, because the disagreements with Protestantism center around the New Testament. When I do, it is to refute some bizarre interpretation offered by a Protestant poster, so it is naturally not from the Deuterocanon.

I remember myself quoting from Ecclesiasticus (Sirach) 15 on Free Will, following Aquinas. The Maccabees are standard prooftext for prayers for the dead and therefore purgatory, see, for example, The Early Church Fathers on Purgatory - Catholic/Orthodox Caucus , especially post 20.

[annalex]

... to elaborate the point already made from scripture, that is.