Incarnation in Matthew is not the news of a unique metaphysics that the world did not know. It is the announcement of a political and ethical counter-reality that the world refused to know. 'Emmanuel' names the divine decison that human violence is to be confronted by the peace of God.
It is promised to Joseph that this gift of a son "will save his people from their sins." What kind of salvation will this be? That question can be answered by asking a prior one - From what kinds of sins will this people be saved from?
Commenting on Micah 1:13, James Mays says that 'the chariot is the chief sin' of the people of Israel. Their militarization, their excessive accumulation of weaponry to secure their "vital interests", is a direct affront to the way that Yhwh would have them walk. In Isaiah 2, the prophet says that Israel's God has rejected his people because "their land is filled with horses, and there is no end to their chariots." Israel's desire to be like the nations around them extended to their resolution to violence. Like all of us, they were determined to keep what they had and regain what they once had, and would use force as the chief means of doing so. It is in this force that their trust lay.
Jesus is given to save people from such trust. He is given as a sign that there is an alternative way to live in a world that has been ubiquitously "reinvested with the truth of violence". He is given as the embodiment and teacher of that way. He is that way, and those who read and hear this gospel are called to follow him.
Behold, a virgin shall conceive and bear a son, and shall call his name Immanuel.
These words were originally spoken to King Ahaz, mentioned already in Matthew's gospel as a descendant of David and therefore an ancestor of Jesus. Jerusalem was under threat, yet in the face of Syrian violence the people of Israel were told to trust not in their military might but in their God, whose presence alone could make for peace. The people of Israel quite rationally refused such risky trust, yet their commitment to the way of violence caused them to suffer the violence of various empires. "They sow the wind and reap the whirlwind."
It is into a sea of violence that Jesus is plunged. The salvation that he will secure for his sinful people can only be constituted by a parting of this sea by the peaceable hand of God.
The Way formed by this parting is where Jesus is, and it is where the church must be too if she is to live and preach the salvation that is meaningless without discipleship.