roll of a book - a book formed of prepared skins made into a roll. Compare “volume of the book,” that is, the Pentateuch (Psa 40:7). It does not follow that his prophecies were not before committed to writing; what is implied is, they were now written together in one volume, so as to be read continuously to the Jews in the temple.
against ... nations - (Jer 25:15, etc.).
from ... days of Josiah - (Jer 25:3). From Josiah’s thirteenth year (Jer 1:2).