"... By quoting the text, the narrator "forces" the reader to "listen" to the Jesus-story in light of the promised "Emmanuel". We have here a clear form of reader guidance. By giving an explicit text (Isaiah 7:14), the narrator unfolds a dynamic reading that is difficult to control. The "intrusion" of the old text into a new literary context may induce the reader to reflect and meditate on possible interconnections. Some ambiguities of the Hebrew version are absent in the Greek text. A vague messianic understanding can be glimpsed in the way the child is introduced. Unlike the Hebrew text, the Greek highlights the distinctive character of the child in a very specific way: he has the ability to distinguish good from evil before he knows either (LXX Isaiah 7:15-16). As Martin Rosel has pointed out, the Septuagint version implies an understanding of the child as a heavenly gifted figure. Although other textual elements from the Isaiah context may enrich the interpretation of the Matthean narrative, the narrator makes sure that no reader misses the main point: the narrative makes Scripture "complete" ..."

Mayordomo, Moisés "Matthew 1-2 and the Problem of Intertextuality" in Claire Clivaz, et al. (eds.), Infancy Gospels. Stories and Identities (pp. 272-273) Mohr Siebeck, 2011

"... Matthew’s rendering of the LXX’s Parthenos from Isaiah 7:14 ('A virgin will conceive and bear a son' [Matthew 1:23]) remains a site of popular piety and scholarly debate. The Hebrew word translated by parthenos in the LXX is ’almah, which is used in the Tanakh in Isaiah 7:14 and six other times (Genesis 24:43; Exodus 2:8; Psalm 68:26; Proverbs 30:19; and Song of Solomon 1:3; 6:8) in the sense of “a young woman” but does not necessarily suggest “virgin.” The Greek Parthenos does not, for the LXX, necessarily connote “virgin,” although that is the predominant translation. It appears in Genesis 34:3 in reference to Dinah, who had just had intercourse with Shechem. The Hebrew term betulah, used more than fifty times, including several times in Isaiah, usually (but not always) carries the technical sense of “virgin.” Thus, for the Hebrew text of Isaiah 7:14, and perhaps even the Greek text, the prophet is saying, “The young woman is pregnant” There is no reason to presume her pregnancy was miraculous ..."

Levine, Amy-Jill & Brettler, Marc Zvi The Jewish Annotated New Testament (p. 4) Oxford University Press, 2011