Coco,
Did I overlook it, or has anyone mentioned 2 Peter 3:15-16?
15 Bear in mind that our Lord's patience means salvation, just as our dear brother Paul also wrote you with the wisdom that God gave him. 16 He writes the same way in all his letters, speaking in them of these matters. His letters contain some things that are hard to understand, which ignorant and unstable people distort, as they do the other Scriptures, to their own destruction.
That's what's used to put Paul's writings on a par with the OT.