In the twenty-first chapter of the third book Against Heresies, St. Irenaeus of Lyons addresses the translation of Isaiah 7:14 among Ebionites and Jews. In doing so, he underlines the antiquity and importance of the Greek translation of the Old Testament as inherited by the apostolic Church.
By the end of the second century (A. D.), two alternative Greek translations of the Hebrew scriptures had been composed. Noting the aforementioned passage in the prophet Isaiah, Irenaeus comments on both:
God, then, was made man, and the Lord did Himself save us, giving us the token of the Virgin. But not as some allege, among those now presuming to expound the Scripture, “Behold, a young woman shall conceive, and bring forth a son,” as Theodotion the Ephesian has interpreted, and Aquila of Pontus, both Jewish proselytes. The Ebionites, following these, assert that He was begotten by Joseph; thus destroying, as far as in them lies, such a marvelous dispensation of God, and setting aside the testimony of the prophets which proceeded from God.1
These later, Jewish translations are now commonly known as Theodotion and Aquila. The work of Jewish scholars a century after the advent of the Christian faith, both editions agree that Isaiah refers merely to a young woman—almah in Hebrew—and not necessarily a virgin (although it does not exclude such an interpretation). But the Septuagint or “Old Greek” scriptures, done by Jewish scribes in Alexandria between the third and first century B. C., translate the Hebrew word as parthenos—virgin. Irenaeus insists that Christians should prefer (in opposition to heretics) the earlier translation of the Septuagint, one done without obvious bias or agenda:
For truly this prediction was uttered before the removal of the people to Babylon; that is, anterior to the supremacy acquired by the Medes and Persians. But it was interpreted into Greek by the Jews themselves, much before the period of our Lord’s advent, that there might remain no suspicion that perchance the Jews, complying with our humor, did put this interpretation upon these words. They indeed, had they been cognizant of our future existence, and that we should use these proofs from the Scriptures, would themselves never have hesitated to burn their own Scriptures, which do declare that all other nations partake of life, and show that they who boast themselves as being the house of Jacob and the people of Israel, are disinherited from the grace of God.2
As certain heretics, along with the Jewish people, were refusing to acknowledge Jesus as the true Christ or Messiah of Israel, Irenaeus efforts to refute their claims on a single point: the antiquity and truth of the virgin birth. In order to bolster his claims, he appeals to the Septuagint as a superior, scriptural account. This leads naturally to a brief detour relating the history of the translation:
For before the Romans possessed their kingdom, while as yet the Macedonians held Asia, Ptolemy the son of Lagus, being anxious to adorn the library which he had founded in Alexandria, with a collection of the writings of all men, which were of merit, made request to the people of Jerusalem, that they should have their Scriptures translated into the Greek language. And they—for at that time they were still subject to the Macedonians—sent to Ptolemy seventy of their elders, who were thoroughly skilled in the Scriptures and in both the languages, to carry out what he had desired. But he, wishing to test them individually, and fearing lest they might perchance, by taking counsel together, conceal the truth in the Scriptures, by their interpretation, separated them from each other, and commanded them all to write the same translation. He did this with respect to all the books. But when they came together in the same place before Ptolemy, and each of them compared his own interpretation with that of every other, God was indeed glorified, and the Scriptures were acknowledged as truly divine. For all of them read out the common translation in the very same words and the very same names, from beginning to end, so that even the Gentiles present perceived that the Scriptures had been interpreted by the inspiration of God. And there was nothing astonishing in God having done this—He who, when, during the captivity of the people under Nebuchadnezzar, the Scriptures had been corrupted, and when, after seventy years, the Jews had returned to their own land, then, in the times of Artaxerxes king of the Persians, inspired Esdras the priest, of the tribe of Levi, to recast all the words of the former prophets, and to re-establish with the people the Mosaic legislation.3
This account is similar in most respects to that shared by St. Justin Martyr in the same century.
In summary, Irenaeus explains how seventy Jewish scribes were sent to Alexandria to translate their own interpretation of the Hebrew scriptures. And when they compared their finished texts, it was discovered that each were identical. This, Irenaeus emphasizes, was seen to be miraculous even among the unbelievers in Egypt: The translation and interpretation of the scriptures into Greek was itself inspired by God. Irenaeus compares this miracle to the restoration of the scriptures in the time of exile. And if the Greek Old Testament was divinely-inspired, how could any faithful person—whether Christian or Jewish—discount its claims? He then compares the preservation of the scriptures in Egypt—in the translation of the Septuagint—with the preservation of Israel in the same, as well as Christ’s own protection there during Herod’s campaign of infanticide (Against Heresies 3.21.3).
Summarizing his arguments, Irenaeus concludes that both Jews and Ebionites should reject the interpretations of both Theodotion and Aquila on this point—the virgin birth of Jesus Christ—since the Greek of the Septuagint was superior in both its antiquity and divine provenance:
[T]ruly these men are proved to be impudent and presumptuous, who would now show a desire to make different translations, when we refute them out of these Scriptures, and shut them up to a belief in the advent of the Son of God. But our faith is steadfast, unfeigned, and the only true one, having clear proof from these Scriptures, which were interpreted in the way I have related; and the preaching of the Church is without interpolation. For the apostles, since they are of more ancient date than all these [heretics], agree with this aforesaid translation; and the translation harmonizes with the tradition of the apostles. For Peter, and John, and Matthew, and Paul, and the rest successively, as well as their followers, did set forth all prophetical [announcements], just as the interpretation of the [seventy] elders contains them.4
For the one and the same Spirit of God, who proclaimed by the prophets what and of what sort the advent of the Lord should be, did by these [seventy] elders give a just interpretation of what had been truly prophesied; and He did Himself, by the apostles, announce that the fulness of the times of the adoption had arrived, that the kingdom of heaven had drawn nigh, and that He was dwelling within those that believe on Him who was born Emmanuel of the Virgin.5
For Irenaeus, this was ultimately a matter of sacred and apostolic Tradition. Since the apostles had themselves shown a preference for the words of “the seventy,” so too should all Christians after them. This drew a clear line in the sand between the Ebionites and the orthodox, and further enshrined the obvious differences between Christians and Jews on the person of Jesus Christ—from birth to resurrection.