In general, Hebrew is more polyvalent than Greek. Thus, the Hebrew text of Scripture is often ambiguous and could be taken in various ways. We might say that without further information we are not sure how we should take it. For example, Ex 3:14 could mean, “I am who am” or “I will be who I will be.” Could be present tense or future tense.
Now, the New Testament more often than not cites not the Hebrew text but the Greek translation called “Septuagint” (LXX for short). In face, the NT cites the LXX 5 out of 6 times. Unsurprisingly, the LXX often disambiguates the Hebrew. Example: Should we read Is 7 as “virgin will give birth” or merely “young lady will give birth”? The LXX specifies “virgin.” Again, is the upshot of Gen 3:15 “they (the seed) will crush your (serpent’s) head” or “he (a coming male) will crush your head.” The Hebrew does not make the discernment; many scholars therefore conclude that “they” conveys the meaning better, “they” meaning the “sons and daughters of Adam.” The LXX, however, unequivocally states “he” (masculine pronoun referring to the neutral “seed”).
A tension may arise. Someone will pine for the plasticity of the Hebrew while another may prize the specificity of the LXX. We may, in fact, hold both but differently.
Regarding Gen 3:15, the LXX happens to give the Christian specificity before Christ: “he will crush your head.” Christians believe that only Jesus Christ, God and man, can crush the head of the serpent with his own power. However, the plastic force of the Hebrew is not thereby nullified. It can still carry through its potential ambiguity, ordered or disciplined by the Greek specificity. The LXX, read in light of the NT, specifies the chief conqueror, Christ Jesus. But the Hebrew allows us also to read “the sons and daughters of Adam,” on the proviso that these are “in Christ” crushing the serpent with him. Note: Several of the Targumim reflect exactly this kind of synthesis among the Jews!
Perhaps, also, the Hebrew in Is 7 can indicate both virgin and “young lady.” It clearly means “virgin” because of the NT confirmation. Perhaps, also, it can be a word of consolation, a sign, already for the king, promising him a son (Hezekiah). Still, this sign is not exactly “as deep as hell, as high as heaven.” Thus, even the Hebrew text signals something more remarkable than a mere sign to Ahaz. It is unreasonable to read the text as regarding merely a “young lady,” as Justin the Martyr pointed out centuries and centuries ago.
Still, the Hebrew ambiguity cannot always carry through. God reigns above all times, not being at all bound by measurement. Thus, we ought not read “I will be who I will be” in the natural sense such a locution suggests, namely, that God is in time.