The Dead Sea Scrolls are the earliest Hebrew scriptures we have, predating the Masoretic texts by several centuries. They show that the Hebrew texts have altered very little since the time of the Qumran sect, although there are some exceptions.
Robert Eisenman says, in The Dead Sea Scrolls and the First Christians, page 38, that 2 Maccabees has a patently similar orientation to Qumran literature, yet it has not been found there. He also notes that Josephus did not know of 2 Maccabees, concluding that it was either not known in Palestine, or not yet written.
Randall Price says, in The Secrets of the Dead Sea Scrolls, page 147, that scroll 4QDeutj, Deuteronomy 32:8 agrees with the LXX ("sons of Israel"), but not the Masoretic Text ("sons of God"). In 4Qexoda, Exodus 1:5 records "75 descendants of Jacob" (agreeing with the LXX; cf. Acts 7: l4) against the Masoretic Text's “70 descendants.” The Paleo-Exodus Scroll (4Q22) shows expansions of the text like that in the Samaritan Pentateuch.
Price says that six copies of Jeremiah recovered from the caves have the longer form of the text in agreement with the Masoretic text, but two have the shorter form in agreement with the Septuagint. They also lack words, names, and sentences and exhibit a different sequence in some places. Before the discovery of these texts there was no evidence for the existence of a shorter Hebrew variant other than the LXX.
On page 149, Price cites Emanuel Tov:
In proto-Judges, a portion from chapter 6 [of the biblical Judges] is
missing – a whole paragraph. It is in our present Hebrew Bible, and
also in English translations, but it is a paragraph which had puzzled
scholars for centuries because it seems to be out of place. Suddenly
we found this fragment at Qumran, in which there is a text of Judges
that doesn't have this paragraph. The text reads better without it.
It helps us understand that at some point in the transmission of the
text this paragraph was added, but the book was already circulating in
another form before it was.
On page 148, Randall Price says of the Samuel A Scroll:
The Samuel A Scroll (designated 4QSama-c or 4Q51-53) is especially interesting because it contains textual variants that appear to support many of the Septuagint deviations from the Masoretic Text. This was important because it provided scholars with an example of the kind of Hebrew version that was behind the Septuagint.
This Scroll also has another exceptional feature: it contains a passage that was completely missing from the Masoretic Text bur was apparently known and used by Flavius Josephus in his Jewish Antiquities (6.69-71). This text mentions Nahash the Ammonite, whose story is given in the Bible in 1 Samuel 11 : l-6.
He says some of the Torah Scrolls expand on the biblical text, for example in the Rewritten Pentateuch (4Q364-367). Others are retellings of the biblical account, such as the Genesis Apocryphon, retelling the story of Abram and Sarai in Genesis 12:10-13 (1Q20 19:14-20) or the story of the flood (4Q252).
On page 381, Price says that the presence among the collection of a horoscope text, a physiognomy text (discerning a person's nature from his or her physical appearance and mannerisms), a chiromancy text (palmistry), and a brontologion text (prediction of the future based on where thunder is heard in the heavens) affirms their use in Judaism prior to the rabbinical period, after which time they were forbidden.
The full importance of the Dead Sea Scrolls for apologetics has not yet been determined. At one stage, it was suggested that a tiny scrap of text was from Mark's Gospel, but that thesis has been dismissed as speculative. There are scrolls that might have been precursors to the beatitudes of Matthew's Gospel, but we will see in the future how secure that hypothesis is.