The Septuagint … (or “LXX“, or “Greek Old Testament“) is an ancient translation of the Hebrew Bible and some related texts into Koine Greek, dated as early as the late 2nd century BCE. It is quoted in the New Testament, particularly in the writings of Paul the Apostle, and also by the Apostolic Fathers and later Greek Church Fathers, and continues to serve as the Eastern Orthodox Old Testament.
When I first attended an evangelical theological seminary, if and when the Septuagint was mentioned, it was only to disparage it. Time was spent in Old Testament classes explaining why Christians should only use the Masoretic Text. Only in a couple of classes was there a grudging admission that the Septuagint was quoted in the New Testament particularly by Saint Paul, as the Wikipedia article quoted above mentions.
In fact, I have now realized that there were some ideas that did not make sense, given what else I also have learned about history. Great arguments were made in favor of the Masoretic Text, almost as though the Septuagint text was somehow deficient. But, the Jews of the first-century regarded the Septuagint as being a miraculous translation in which God ensured that the Hebrew was translated correctly. In other words, modern evangelicals were arguing that Jews were wrong about the accuracy of the translation of their own Scriptures!
More than that, as was admitted in the seminary, the Septuagint was quoted in the New Testament in the same way that the Masoretic Text was quoted. In other words, the very Apostles from whom we have received the faith obviously considered that the Septuagint was a very appropriate and sufficiently accurate translation of the Old Testament to use in quotes that set the doctrine that we believe as Christians. Let me repeat that, the very Apostles from whom we have received the faith obviously considered that the Septuagint was a very appropriate and sufficiently accurate translation of the Old Testament to use in quotes that set the doctrine that we believe as Christians. Somehow, the seminary was able to argue that the Septuagint was not as good as the Masoretic text even while they argued in favor of those doctrines that were supported by quotes from the very Septuagint they disparaged.
Finally, it was the Septuagint that was the Bible that New Testament Christians knew, outside of the Israeli Christians. Somehow, the faith in which we believe was spread, explained, developed, and theologized in Greek, not in Hebrew. It was that very Septuagint Bible that has, in many ways, formed the foundations of our faith, along with the memoirs of the Apostles (the Four Gospels) and their explanatory letters, which we call the epistles.
Does this mean that the Septuagint is a perfect translation? No, Saint Athanasius–who helped us to define the Trinity–also commented that some of the books in the Septuagint Old Testament appeared to be less reliable than others. But, what this does mean is that the view of the Septuagint that I was taught in seminary was inadequate. The Septuagint contains the foundations of our faith. It is a reliable translation because both the Jews and the Early Christians said so and used it that way. Given that the Jews saw the Septuagint as a reliable translation, this means that we need to stop demeaning or denigrating the Septuagint. To do so is to mount the argument that the Jews were mistaken about their own Scriptures and that the Apostles were mistaken in their quoting the Greek translation of the Hebrew Scriptures. But, as I pointed out earlier, this questioning of the Apostles brings into question our Christian doctrines.
Thus, it is no surprise that the Orthodox Church has declared that the Septuagint is the version of the Old Testament that we support.