A long standing argument between Christian and Rabbinical Jewish theologians which revolves around the Books of Isaiah and Matthew have been an unsettled one. The issue of whether or not Isaiah spoke of a virgin giving birth to a child has put the divine messianic nature of Jesus' birth in question according to Rabbinical Jews; but a closer look at these passages may reveal what both groups may have failed to acknowledge.
For the Christian authorities on the Bible, the passage in question starts with the Book of Matthew in the New Testament. The argument here is that Matthew has connected the birth of Jesus and his mother's virginity to a prophecy found in the famous Isaiah 7:14 verse. Matthew reads,
All this took place to fulfill what the Lord had spoken by the prophet, 'Behold, the virgin shall conceive and bear a son, and they shall call his name Immanuel (which means, God with us).'"
Christian theologians have no problem with this passage since they argue that the Greek word used here for the bolded word is Parthenos. They proclaim that the Greek word exclusively means virgin, so when Matthew used it, that's what the translation called for. They also argue that the word Parthenos was also used in the Greek Septuagint.
The Septuagint was a translation of the Old Testament from its original Hebrew language into Greek a few centuries before Jesus' time. Since the Septuagint, which was translated by Jews contained the word Parthenos in Isaiah 7:14, Christian authorities argue that even the translators saw the woman as being a virgin giving birth.
However, Rabbinical Jewish authorities disagree with this Christian notion. Rabbinical authorities argue that the Hebrew text of Isaiah 7:14 never called for a virgin birth. They translate the text as such,
Behold, the young woman shall conceive and bear a son, and shall call his name Immanuel."
As opposed to the above Matthew text, this version uses the words young woman instead of virgin. Rabbinical authorities argue that the Hebrew word Isaiah used was Almah, which translates to young woman and that the Matthew text is a corruption. It should also be noted that many Rabbinical authorities reject the Greek Septuagint for linguistic reasons.
They also argue that if the prophet Isaiah wanted to say that the woman was a virgin, he would have used the Hebrew word Betoolah, which better translates to virgin. It should be noted that a virgin within these ancient periods signified an unmarried woman, but in certain cases it referred also to sexual purity. This particular argument deals with the latter.
So which authority was accurate? It seems that a closer examination of both the Isaiah and Matthew passages in their ancient languages reveal that both authorities were both correct, and incorrect at the same time. It appears that the main problem plaguing this argument was a typical case of mistranslation.
The Christian authorities were indeed correct that Mary, the mother of Jesus according to Matthew was a virgin. However, they were incorrect in contending that the Greek word Parthenos is what Matthew was using to say virgin. Matthew revealed that Mary was a virgin based on a common phrase that was used at the time. The same chapter reads,
He (Joseph) took his wife, but knew her not until she had given birth to a son. And he called his name Jesus."
The phrase, 'Knew her not' referred to not having sexual relations with her. Matthew 1:18 already said that Mary was impregnated divinely by the Holy Spirit so with this information, it's known she was sexually pure. The word Parthenos was not referring to sex, it was quoting Isaiah directly as young woman.
Evidence of this is found in Thayer's Greek-English Lexicon. According to Thayer's, the word Parthenos had three meanings instead of one. A virgin, an unmarried woman and a young woman. The Rabbinical authorities were correct concerning Isaiah using the word Almah as young woman, but were incorrect in insinuating that Matthew was a corruption, since the meaning of Parthenos Matthew used was the same as Isaiah's.
This also explains why the Greek Septuagint used this word. They weren't translating Isaiah 7:14 as virgin, but as it was found in the Hebrew as young woman. A rule for all translators is to identify all possible meanings of a word as well as understand the context surrounding the passages.
In summary, neither Isaiah nor Matthew focused on the sexual purity of the woman in this particular prophecy. Instead, Isaiah focused on the child who would be born, and Matthew focused like wise on the fulfillment of this child who was born of the title Immanuel which is, God with us.