The discovery of the Dead Sea Scrolls beginning in 1947 in the caves near Qumran by the Dead Sea was one of the most significant archaeological finds of the twentieth century. Among the scrolls were copies of every Old Testament book except Esther, dating from approximately 250 BC to 68 AD.
Before this discovery, the oldest complete Hebrew Old Testament manuscript was the Leningrad Codex, dated to approximately 1008 AD. The Dead Sea Scrolls provided a test: compare the Qumran manuscripts with the medieval Masoretic text and see how much had changed over roughly 1,000 years of transmission.
The result was stunning. The Great Isaiah Scroll (1QIsaa), a complete copy of Isaiah dated to approximately 125 BC, was compared word-by-word with the Masoretic text. The agreement was approximately 95%, with the 5% variation consisting almost entirely of spelling differences, minor word order changes, and scribal slips — none affecting meaning or doctrine.
This demonstrated that Jewish scribes had transmitted the text with extraordinary care across a millennium. The Masoretic tradition of counting every letter and word in each book was an effective quality control mechanism.
For apologetics, the Dead Sea Scrolls confirm that the Old Testament text — including the messianic prophecies in Isaiah 53, Daniel 9, and elsewhere — existed in their current form centuries before Christ, eliminating any possibility that these prophecies were written or modified after the fact.