Is Isa 7:14 prophetic?

i) Isa 7:14 is a classic messianic oracle, made even more famous by Handel's Messiah. It is, however, common to the claim that the Christian interpretation (or Matthew's interpretation) is anachronistic. The conventional liberal reading identifies the woman as either Isaiah's wife or the wife of Ahaz. On that view, the child is either one of Isaiah's sons or Ahaz's. That's said to fit the context, whereas the Christian interpretation is said to rip the passage of context.

There's some value in discussing this. For one thing, During the dry seasons of life, a Christian can experience doubts. When he's in that mood or state of mind, he may wonder if he hasn't defended the Christian interpretation from mere tradition or wishful thinking.

ii) As I've pointed out on more than one occasion, Alec Motyer has demonstrated that it's actually liberal scholars and commentators who take the passage out of context by artificially separating this particular oracle from the larger context. But the son is part of an ongoing motif, that carries all the way through to chap. 12:

http://www.tyndalehouse.com/TynBul/Library/TynBull_1970_21_05_Motyer_Isaiah7_14.pdf

The advent of the son extends into future vistas well beyond the immediate crisis in chap. 7.

iii) Of course, Motyer is evangelical. Perhaps of more interest in that regard is Brevard Childs. He was one of the premier OT scholars of his generation. Unlike Motyer, he was not evangelical. But that makes his interpretation all the more striking:

The mysterious name of Immanuel in 7:14 receives clarification in two passages in chap 8 that belong roughly to the same period of the Syro-Ephraimite crisis. The judgment announced by Isaiah will come and cover the whole land, but the remnant has hope because the land belongs to Immanuel (8:8). Again in 8:9ff., in spite of the evil plans of distant nations, their counsel will not prevail because God has so willed it through Immanuel (v10). In sum, Immanuel is no longer the unborn child of 7:14, but the owner of Israel's land and the source of the divine force that brings the plans of the conspiring nations to naught (Ps 2:1ff.). Notwithstanding the extraordinary mystery and indeterminacy surrounding the giving of the sign of Immanuel, there are many clear indications that it was understood messianically by the tradents of the Isaianic tradition, and shaped in such a way both to clarify and expand the messianic hope for every successive generation of the people of God. B. Childs, Isaiah (WJK 2001), 68-69.

Earlier we describe the movement from the promise of Immanuel in 7:14 to a clearly messianic interpretation of his role in 8:8,11. Now the son is described as coming in the period of Israel's deepest humiliation: "The people walking in darkness have seen a great light. The royal titles of kingship are conferred upon him: "Wonderful Counsellor, Mighty God, Everlasting Father, Prince of Peace." Each name brings out some extraordinary quality of the divinely selected ruler…The description of his reign makes it absolutely clear that his role is messianic.

To summarize: There is a narrative movement from 7:1-9:6 that portrays the rejection of the promise of God by the house of David and the resulting destruction of the people of God as divine hardening takes effect. Conversely, there emerges the hope of a faithful remnant, adumbrated by Isaiah's own experience of death and rebirth in chap. 6, and foreshadowed by the sign of Immanuel. This unfolding presentation of the entrance of God's rule in the midst of terrifying disasters culminates the history of the Syro-Ephraimite crisis with the messianic promise of chap. 9 and anticipates its ultimate expansion in chap. 11 (80-81).

In chap 7 the historical context of the Syro-Epharaimite war of 734 is absolutely crucial for its interpretation and the historical details have been assigned a centrality by the biblical text itself. Again, in chap 9 the initial background for the messianic light that suddenly breaks forth (v1) appears to be the Assyrian conquest of Galilee, but even here very shortly the messianic promise far transcends the initial 8C setting. When one comes to chap 1, the emphasis on v1 falls on the new life sprouting from the mutilated house of David (101).

So Childs arrives at the same basic interpretation as Motyer, based on thematic intertextual links, despite the fact that he doesn't share Moyter's evangelical presuppositions. 

iv) But suppose, for discussion purposes, that we grant the liberal identification, yet with a twist. Who was Isaiah referring to? This goes to theories of reference. What fixes the referent? 

To take a comparison, people sometimes confuse identical twins. Take twin brothers. Let's call them Ryan and Brian. Suppose I'm talking to Ryan, but he has to break off the conversation to check on something in his bedroom. He reemerges a minute later, so I resume the conversation, picking up where I left off.

Only it's a case of mistaken identity. It's not Ryan who just came out of the bedroom, but Brian. I can't tell the difference. They look alike, sound alike, dress alike. Same haircut. Comb it the same way. So I talk to Brian as if I'm talking to Ryan, since I think I'm still talking to Ryan.

Who am I actually speaking to? My comments are physically addressed Brian, but intentionally addressed to Ryan. My words are directed at Brian, but my thoughts are directed at Ryan. I'm looking at Brian, my voice is pointed at Brian, yet he's not the mental object of my communication. In effect, Brian functions as a stand-in for Ryan. 

Even if (ex hypothesi) there's a sense in which the son in 7:14 is a son of Ahaz or Isaiah, he could still function as a placeholder for a more distant referent–apropos my illustration of twin brothers. 

v) A critic might object that that's ingenious special-pleading. To which I'd say two things:

I've already documented that the son in 7:14 is part of a royal messianc sonship motif which extends will beyond the topical crisis chap. 7.  

In addition, there's extrabiblical evidence for premonitions and prophetic dreams. Admittedly, these are short-term rather than long-term, yet the principle is the same. Some people are enabled to foresee the future. Glimpses of the future are revealed to them.