No other book of the Old Testament contain as many prophecies as the Scroll of Isaiah. In fact there are so many that it was proven beyond a shadow of a doubt that Isaiah most probably was written in its final form around 400 A.D.
The scroll they found was a copy, copied no later than 140 B.C. and possibly much earlier, and with that discovery a hundred years of critical biblical analysis was rendered obsolete. They found fragments of most of the Old Testament books, but also much material about day-to-day life around Jesus time, which helped in understanding many terms in the Hebrew language, the meaning of which had been lost.