Without citing the bible, what marks the bible as the one book with God's message?

[RBP3280]

That's part of the christian establishment legend, but not actually true.  The romans couldn't have told you the difference between a christian, a jew, or any other heathen.  

Pliny the Younger in his letter to Trajan, which would have been contemporaneous with 2 timothy, makes that clear.  Roman persecution comes much...much later, in the 300's, responding to the political threat that christianity had since become.

No the persecution of Christians ended in 300 AD when Constantine endorsed Christianity. That is when the first counsel was assembled to decide what would be included in the New Testament. Prior to that the Jewish leadership actually pushed Rome to destroy the Christian movement.