If the scrolls do not overturn the Bible, they richly illuminate it in two ways scholars did not expect.
First, they vindicated the ancient Greek translators. For centuries, where the Septuagint, the pre-Christian Greek Old Testament, differed from the Hebrew, scholars often assumed the Greek translators had paraphrased or erred. The scrolls showed that in a striking number of places the Septuagint was faithfully translating a genuine, older Hebrew wording that had simply not survived elsewhere, now found at Qumran. A famous case is Deuteronomy 32:43, where a Qumran Hebrew copy contains the fuller line "let all God's angels worship Him," matching the Greek that the New Testament quotes in Hebrews 1:6 (Deuteronomy 32:43, Berean Standard Bible, which follows that older reading; the King James and American Standard Versions, resting on the Masoretic text, do not carry the line at all, which is itself the point), evidence that the New Testament's Greek Old Testament rested on a real Hebrew text, not a loose one.
Second, they lit up the world of the New Testament. The scrolls are the closest thing we have to a firsthand library from the Judaism of Jesus' own century, its ways of reading Scripture, its calendars and purity, and above all its intense hope for God's decisive act and his anointed ones (messiahs). Scholars have found illuminating parallels to John the Baptist's desert ministry, to phrases in the Gospels and Paul, and to early Christian expectation. The careful point is parallel, not dependence: the shared language shows Jesus and the first Christians speaking the living religious idiom of their time and place, it does not show, as some have sensationally claimed, that Christianity was secretly "copied" from the Essenes. The scrolls give the Bible its context, in the very words of the people who lived alongside its events.