Well first we start with the Septuagint.
The Septuagint LXX:
Greek and English
by Sir Lancelot C.L. Brenton
published by Samuel Bagster & Sons, Ltd., London, 1851
http://www.ccel.org/bible/brenton/
http://members.ozemail.com.au/~pballard/lxx.html
New English Translation of the Septuagint
http://ccat.sas.upenn.edu/nets/
Septuagint From Wikipedia, the free encyclopedia.
http://en.wikipedia.org/wiki/Septuagint
What is the Septuagint?
The simple answer is that the Septuagint is the Greek translation (from Hebrew) of the Jewish Scriptures, the Christian Old Testament.
Unfortunately, several revisions of this translation were made, and different scholars mean different things when they refer to the 'Septuagint'.
Some mean the original translation of the Torah, which was done in the third century B.C. Some mean the original translation of the entire Old Testament plus Apocrypha, which was done over the next century or so. But so many revisions have been made, that none of these these original translations exist. So some scholars will use 'Sepatuagint' to refer to a particular revision of the translation. But even these can only be reconstructed from what manuscripts we have. So still other scholars will use 'Septuagint' to refer to a particular manuscript of the Septuagint.
So be wary when you read about 'The Septuagint'. It can mean different things to different scholars. Fortunately, however, the general features of the Septuagint (such as those discussed in this article), are common to whatever 'Septuagint' one is talking about.
Why the name 'Septuagint'?
According to an ancient legend in a document known as the Letter of Aristeas, the original translation was done by 70 Jewish scholars. This led to the name 'Septuagint', which is derived for the Latin for the word 'seventy'.
Why the abbreviation 'LXX'?
LXX is the Roman Numeral representation for the number 70.
Who used - or uses - the LXX?
The early Christian church was predominantly Greek-speaking, so it used the LXX for its Greek Scriptures. So most Christian writers of the first three centuries - including the writers of the New Testament - generally used the LXX as their Old Testament.
Probably at least partly in reaction to this, Jews stopped using the LXX after the first century AD.
The Western church (the ancestor of the Catholics and Protestants) became Latin speaking, so from the fourth century on it used Jerome's Latin translation ('The Vulgate'). This was based on the Hebrew rather than the LXX.
Why else is the LXX important?
Because the LXX was translated in about 200 B.C., it gives an idea of the state of the Hebrew text at that time. Unfortunately, this can be largely speculation, because until the discovery of the Dead Sea Scrolls, scholars could only guess whether differences from the MT (MT = Masoretic Text, the existing Hebrew text of the Old Testament) were due to errors in translation, or due to the translators working with a different text to the MT.
The majority of the Dead Sea Scrolls (DSS) resemble the MT. But a significant minority (about 5%) are obviously very similar to the Hebrew used to translate the LXX. By showing examples of Hebrew texts which match the LXX, the general effect of the DSS has been to reveal that the LXX was indeed done from a Hebrew text which was different from the MT, and that it was a more accurate translation than had previously been thought.
How significant are the differences?
Not very.
Something we forget, in this age of photocopiers and computers, is that copying documents by hand is a tedious and error-prone process. It is almost impossible to copy a document exactly. (If you don't believe me, try copying this web page word-for-word and see how you go). Therefore errors creep into any text which has to be copied by hand. This process has been observed for every document for which we have multiple copies - religious documents included.
However, the errors are generally very minor - a word missed or misspelled here or there. Generally not even enough to affect the meaning of the sentence, and it is fairly rare for differences in the underlying text to affect the overall meaning of a passage - let alone any Jewish or Christian doctrine.
An exception is the book of Jeremiah, which I will discuss below. (I believe Job is also a similar case).
More significant that the textual differences (that is, differences in the text of the underlying Hebrew) are the differences due to translation. That is, as I've mentioned above, the translation from Hebrew to Greek is of a varying quality. So if you read an English translation of the (Greek) Septuagint, and compare it with a modern English translation of the Old Testament (which is done direct from the Hebrew), then you'll see quite a few differences. These differences often reflect the way the Hebrew was translated into Greek, often losing some of the meaning, or even changing it somewhat.
But doesn't ANY difference affect the reliability of the Bible?
It depends how you understand Scripture.
Some people (including some Christians, most Jews, and nearly all Muslims) understand their Scriptures to be the exact words of God. They believe that their Scriptures have been miraculously preserved to be in exactly the state God created them, because any change would represent the corruption of the word of God.
If that is the view one holds, then differing manuscripts are a serious problem to one's faith.
However, most Christians have (or should have) a more relaxed attitude to Scripture. For a start, the Bible has what we engineers call 'built-in redundancy'. That is, anything important is told more than once. So the Bible (like a machine with 'built-in redundancy') can continue to function (that is, deliver God's word) even when small errors are introduced into the text.
But a more important difference for the Christian is that salvation comes not from obeying the letter of the Law, but through faith in Jesus. So if you are unaware of one of God's laws because it is missing from your Bible, it does not affect our salvation. Because it is Jesus, not our obedience to the Law, which saves us.
For many Muslims and Orthodox Jews (and some fundamentalist Christians), obedience to the exact law is very important. So for them, errors in manuscripts are a serious problem for their faith. The general reaction is to deny that there have been any changes in their Scriptures, but (in all three cases) the evidence is against them.