Again from the aforementioned link.
**Saint Basil the Great in his “Interpretation of Isaiah", p. 464, writes of the allegations of the Judeans (and of Porphyrios), below:
"The Jews are resisting the publication of the Septuagint edition, claiming that the word “Virgin” does not agree with the Jewish view, instead it should be “the Young Maiden”, in that it implies a young woman who is in the prime of her life, and not to a woman who is unfamiliar with wedlock”.*
To which, Saint Basil replied:
"Unless it is a tremendous sign and a display of something different to the commonplace manner of people, what is there so wondrous about one out of many women who cohabits with a man, to become the mother of a child? How then can it also be, for a child born of fleshly desire to be called Emmanuel? (Emmanuel=the Lord is amongst us) So that, if the event was indeed a “sign”, the birth would also be paradoxical. If the manner of the child’s birth was commonplace, it would neither be called a “sign”, nor would the child be called “Emmanuel”. Likewise, if the woman who gave birth was not a virgin, what kind of “sign” would that be? And if the birth was not divine -as many claim- then how is the presence of Emmanuel explained?"*
Essentially, what Saint Basil is saying is: "where is the miracle, if a married woman became the mother of a child?* And if that was considered the “sign” (in other words the miracle), then, thewayit was born must have been uncommon.* If it was the commonplace kind of birth, then it would not have been called a miracle.* If it wasn’t a virgin who was going to give birth, then where is the miracle?"Saint Basil also provides us with other examples: in Deuteronomy 22:27 and Kings III 1:3-4, where virgins are referred to as “maidens”.Even if Isaiah had used the word “almah” instead of “bethulah”, he still implied the same thing, i.e., that a virgin was to give birth to a son. Otherwise, the prophesying of this miracle (the wondrous sign) would not have made any sense. The Septuagint translators had very appropriately translated the word “almah” as “virgin”, because that is precisely what Isaiah wanted to stress: that a woman, who had no carnal relations, was to bear a son. That is what constitutes a miracle and a “sign”.**