Paul was aware he was writing Scripture

He was committing his revelation to writing

Ephesians 3 is a good study of how the Church was founded on the Scriptures, and not the other way around.

In Ephesians 3:1, Paul describes how he received the revelation directly, even though he is technically outside of (what is much later called) the “apostolic succession,” c.f. Galatians 1:1.

In Ephesians 3:1b, Paul writes: “…as I have written briefly (emphasis added)….”

In Ephesians 3:4 the Apostle continues: “When you read (emphasis added) this you can perceive my insight into the mystery of Christ….”

Paul immediately commits his revelation to writing. There is no oral history here.

Part and parcel of this written revelation is the charter of the Church. Paul writes in Ephesians 3:10 that “through the church, the manifold wisdom of God might now be made known….”

The Church was established on the word of God written, which is why, in later years, she could recognize that word when it came time to fix the canon of scripture.