The Great Isaiah Scroll, called such because of its large physical size, is dated by scholars about 150 BC. Prior to its discovery and public revelation in the 1950s, the earliest copies in existence of Isaiah were from about a thousand years later, roughly 900 AD. So with the discovery of the Great Isaiah Scroll, and the other scrolls at the Dead Sea, scholars now had a valid test to determine whether ancient scribes could accurately copy a document by hand for a thousand years.
The result is that there were some changes in spellings as you might imagine, a few easily detectable slips of the pen, but zero content questions. The copying was so accurate as to leave no doubt whatsoever about the accuracy of the text.
Scholars of ancient documents, whether theist or not, recognize that the Dead Sea Scrolls in general, and the Great Isaiah Scroll in particular, show us that the Bible we have today has been copied accurately since it was written.
Interestingly, there is a fascinating internet image of the scroll, which you can find here. The entire scroll can be seen with English subtitles.