In regards to Scripture:
I oversimplified it because it's a peripheral issue. Obviously, scriptures have always been critical to the Jewish and then the Christian faith. What I probably should have written is "a faith based on reading". What I meant by that is that our our modern way of thinking about discipleship and growing in our faith through dedicating ourselves to the study of scripture would never have occurred to the first century Christians. The fact is the first century Christians probably had access to, at best, a single copy of the Tanakh and only the few literate members of the church would be capable of reading it. Thus the concept that a person's faith should be built through daily reading would not have occurred to them. It simply wasn't possible at the time.

In regards to the trinity:
Since defending that view would require being sidetracked and bogged down in a debate on early church history that I don't care to get into, I'll withdraw that claim.

Nevertheless, it is without any doubt that the idea of substitutionary atonement is a development from the second millenium and was developed by Anselm of Canterbury. The writers of the NT would certainly not have recognized that view. If you spoke with Paul or John or any of the apostles about what Christ's death meant, they would have explained that Christ died in order to pay Satan the ransom required to buy us back. Anyone who believes something other than that, does not have a view of salvation that the NT writers would have recognized.

Biblical inerrancy is also later theological development that the NT writers would not have recognized. The Sola Scriptura doctrine that forms the foundation of protestant Christianity is also a late development.

My point is that asking whether the NT writers would have recognized certain doctrines is not a useful question. The question should be "is it true?", not "did people a long time ago believe it?".