There’s a better question...What outside of Scriptures do you consider divine revelation, more importantly God Breathed?
The answer is simple. The Dogmas of the Catholic Church. Inspired, guided and preserved from teaching error by the Holy Spirit. The 3rd Person of the Blessed Trinity. To put it another way: to be transported to the 1st Century, to be present at the writings of the first gospels one would be hard pressed to derive the doctrine of the Trinity simply from the text.
Sure, today we can quote scripture, “In the Name of the Father and the Son and the Holy Spirit,” but by what method would one derive the doctine of the Trinity from that? It’s not unreasonable to believe that these things had to be figured out.
One would have to, of course, accept that doctrine is developed as we come to a fuller understanding. Some would suggest that this represents a repudiation of what came before. That it divorces man from the Word of God. I disagree.It is the fulfillment of what was handed down and thus it is proper that by our faith and our reason we approach a fuller comprehension of the tenets of our faith.
This is especially crucial since the scriptures are not self-interpreting. We all stand on the shoulders of the gospel writers, the early church fathers and others who came before us and helped us grow in our understanding of the Faith. Ultimately that is why Christ left us a Church. To teach. With scripture at its core but never separated from Christ’s Church.
It’s up to each of us and our own individual consciences to either accept or reject that. But ultimately it requires an act of faith. To say yes even if we don’t fully understand.