Isaiah is the first of the great prophetic books, though Isaiah was not the first of the great prophets. The first to have a book named after him was Amos. Neither did prophets such as Amos and Isaiah fulfill their ministries by writing books. Prophets fulfilled their ministry by showing up in a public place such as the temple courtyards in Jerusalem and declaiming to anyone who would listen and also to the people who didn’t wish to listen. You can get an idea from reading the book of Jeremiah,