This is from a lesson I taught on prophecy when I was a NT adjunct at a couple of schools in SW MO. My mind returns to this subject every year at Christmas.
This is a practice of the New Testament writers in how they related to the Old Testament. The term refers to a deeper or fuller sense within the quoted material that might not have been understood by the original author, but is now detectable in the light of the new revelatory fulfillment. This view assumes a divinely intended correspondence between God’s saving activity at different times in the history of redemption. This was practiced by Jewish writers as well as NT interpreters. This view is tied to a belief in the sovereignty of God, the inspiration of the Scriptures and the unity of God’s saving purposes resulting in the interconnectedness of his redemptive acts. To the Christians was the conviction that Christ was the goal of what the OT promised. With these presuppositions, Christians such as Matthew saw correspondences between events of the past and the time of Jesus not as coincidental, but as divinely intended, with the earlier foreshadowing the latter.
The prophet in Isaiah 7 promises as a sign to King Ahaz and the House of David the birth of a son, during whose infancy the two kings feared by Ahaz would be ruined (Syria and Israel). Fulfillment of this passage is required in the immediate future.
Was Matthew wrong to use this verse as a fulfillment of the birth of Jesus? Even Jewish interpreters saw something fuller in this prophecy. The name given to the child, Immanuel, spoke of a later day when God’s presence would ultimately be fulfilled (Day of the Lord). This figure in 7.14 became identified in Judaism as that son of David who would bring the expected kingdom of security, righteousness, and justice. Accordingly, probably sometime in the third century BC, the Greek translators of the OT apparently regarded the passage as having a deeper meaning, yet unrealized. They chose to translate the Hebrew term in Isaiah 7.14 (almah or young woman who may or may not be a virgin), with the Greek term parthenos (more specifically virgin) instead of neanis (young woman) used by later Jewish translators of this passage. This was seen to be understood as a supernatural association brought to mind by the identity and work of this son.