How do Protestants view the prophecy and birth of Jesus

This very question is important for understanding some of the subtleties of how protestants, at least some of them (there are numerous views about this), understand how the Bible works and the art of hermeneutics.

Isa 7:14 is a simple prophecy about a sign concerning the certainty of what was predicted about the future of Judah. The sign itself involves a woman conceiving and giving him the name "Emanuel". The operative word is set out below.

This word "almah" occurs 9 times in the OT and this is the last of them (See Gen 24:43, Ex 2:8, 1 Chron 15:20, Ps 46 (superscription), Ps 68:25, Prov 30:19, SS 1:3, 6:8, Isa 7:14). The meaning of this word is highly debated as to whether it means "young woman of child bearing age", or "young virgin woman". Most of the occurrences are debatable but Isa 7:14 is NOT. It concerns (very probably) Isaiah's young wife (see Isa 8) who had already given birth to a son (Isa 7:3) and as a result of the prophecy would bear a second son. Despite this (to add to the confusion) LXX renders this words, "Parthenos" (= virgin).

Therefore, based on the immediate circumstances in this passage, "almah" does NOT mean virgin. If that had been the extent of the material on this subject, no one would have suggested Isa 7:14 to be a Messianic prophecy.

It is only because of Matt 1:20-23 (and its quoting of the LXX) that a NT writer under divine inspiration takes this OT incident and uses it to become a Messianic prophecy; and in doing so uses a Greek word which definitely means "virgin". In the absence of the NT reference, no ordinary writer would have been justified in making such a Messianic claim but the NT inspired writers can.

The pulpit commentary gives a VERY brief overview of the raging debates around his verse which I have greatly simplified with the simplest solution.

I don't see how one can sincerely call Mahershalalhashbaz the referenced Immanuel, since that prophecy was directed to the house of David, specifically that they would call him that. When otherwise did they, the house of David, ever call Mahershalalhashbaz, 'Immanuel'? How or why also would Isaiah have been calling his own son 'Immanuel' in Isaiah 8:8, given that that would suggest that he was by implication calling his own son 'Mighty God', 'Prince of peace'(Isaiah 9:6), one that should reign(Isaiah 9:7)?

To this latter point also, it should seem that Isaiah was responding to the attempts of Rezin king of Syria and Pekah king of Israel to place a king(other than the house of David) in Jerusalem(Isa 7:6), by referencing the Messianic tones of 2 Samuel 7, and telling them thus of the spiritual kingdom which should someday rule and reign, according to the order of those things as they began(1 Sam. 12:12).

Lastly, this idea should leave the latter phrase of verse 16 to be understood in a context where the land was still occupied by at least one king, namely the king of Judah, the 'forsaking' thereof not to be at all interpreted as referencing the captivity, but the Assyrian occupation, that is, during's Pekah's reign only, the king of Judah still being in the land.

Given this then one is left to interpret Isaiah 7:14 not according to what is possible(as said above Song of Solomon 6:8 already proves it can mean 'virgin'), but what is probable to the context. Would Isaiah really be calling his own son king or God? No, these are two different people being referenced, the first is Messianic and the second is not. I'm not sure I've answered the question with regard to Protestantism, however hopefully I have partly addressed the second.

The key word of Isaiah 7:14 is "sign". Understanding that word will clarify the sign itself.

Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel. Isa 7:14

David was a man after God's own heart [1 Ki 15:3, Act 13:22]. In contrast is this king Ahaz to whom Isaiah is speaking. Isaiah offers him a sign from God, but Ahaz, while feigning piety, rejects it. So, Ahaz rejects Isaiah and now has rejected God. God, however, says He will nonetheless provide a sign.

With that in mind, the question arises what kind of sign from God will this sign be? Some doubt God that a virgin will conceive. Some instead feel that the sign would simply be a young woman getting pregnant in the normal way. But obviously, a normal conception in the normal way can hardly be taken as a sign from Almighty God.

Matthew and countless future Christians understand this. A sign is a miracle, a token, a mark, a signal, a beacon. A sign is not something normal.

So yes, Isaiah 7:14 is a prophecy of Immanuel; that is, God with us who is Christ Jesus.