What's going on here?

An angel of the Lord suddenly appeared to [Joseph] in a dream, saying, "Joseph, son of David, don't be afraid to take Mary as your wife, because what has been conceived in her is by the Holy Spirit. She will give birth to a son, and you are to name Him Jesus, because He will save His people from their sins." Now all this took place to fulfill what was spoken by the Lord through the prophet:

See, the virgin will become pregnant

and give birth to a son,

and they will name Him Immanuel,

which is translated "God is with us."

When Joseph got up from sleeping, he did as the Lord's angel had commanded him. He married her but did not know her intimately until she gave birth to a son. And he named Him Jesus. (Matthew 1:20-25, my bold)

Joseph obeys the angel and names Jesus "Jesus", but Isaiah said "they will name him Immanuel" - there's different names there! What's going on?

Immanuel comes up once in Isaiah 7 (quoted in Matthew 1), and once more in Isaiah 8 (describing the size of the devistation left behind by the Assyrian army - it'll even reach the end of the Immanuel's kingdom).

The whole idea of "Immanuel" is rather scary - judgement is sure to happen.

• The people of Israel are shocked that Moses has spoken with God and not died.
  

  Look, the LORD our God has shown us His glory and greatness, and we have heard His voice from the fire. Today we have seen that God speaks with a person, yet he still lives. But now, why should we die? This great fire will consume us and we will die if we hear the voice of the LORD our God any longer. For who out of all mankind has heard the voice of the living God speaking from the fire, as we have, and lived? (Deuteronomy 5:24-26)

  In verse 28 God affirms that they are speaking truth.

• Unclean things defile the tabernacle and that means death - nothing unclean or sinful can go near it.
  

  You shall keep the people of Israel separate from their uncleanness, lest they die in their uncleanness by defiling my tabernacle that is in their midst. (Leviticus 15:31)
  The Word became flesh and tabernacled among us. (John 1:14)

Something needs to happen if we have Immanuel: "God with us", and we survive that encounter. We need Jesus: "God saves" to enable God to be with us, without killing us. It is only by him saving us from our sins that we can have Immanuel.

Yes Jesus is called Immanuel - by Christians over the centuries - but not by Joseph, who gives Jesus the name that is the key to unlocking the other stuff. Not Terrance the teacher, Henry the healer, Percy the prophet, nor Mike the miracle worker, but Jesus the saviour. He is those other things, but that's not his badge, not how God, through the angel and Joseph, wanted him to be labelled!