The word was spread by believers carrying individual copies of manuscripts long before printing presses or halls full of scribes came along.
The closest thing to a book at that time was the scrolled codex of the Jews. That was what was carried as “scripture” by the believers for several centuries.
Remember about the Bereans? They were noted for searching the scrolls to verify the truth of the apostles words.
“The closest thing to a book at that time was the scrolled codex of the Jews. That was what was carried as scripture by the believers for several centuries.”
Codexes aren’t scrolls.