The passage
      v18. Mary is engaged to Joseph. In Jewish custom this includes all the responsibilities of marriage, except that the girl stays in her parents' home for about a year before the marriage and its consummation. Mary conceives through the action of the Holy Spirit. So, a divine creative act inaugurates the messianic age through the agency of the Spirit. With these words Matthew defines Jesus' origin.
      v19. Originally, stoning was the punishment for unfaithfulness, but by this time, public humiliation and divorce were the usual method. Joseph kindly set about to divorce Mary "quietly" (privately).
      v20. In typical Old Testament style, God conveys his word to his people through a "messenger (angel) of the Lord." In Joseph's case, God's word comes to him in a dream, certainly not an unusual means for an Old Testament saint. Joseph must marry Mary, for the child must be included in the Davidic line. In Jewish custom, for Joseph to acknowledge the child as his, makes the child, like Joseph, a "son of David". Such acknowledgment fully includes the child in the family.
      v21. In the Old Testament, the giving of a name, and particularly a name given by God, is full of meaning. The name "Jesus" is Greek for Joshua, and means "Yahweh is salvation." In Hebrew, the word "Jesus" actually sounds like "he will save". So, the name is full of meaning; Jesus is the messiah who will save his people. The people he will save is Israel, but this does not exclude the Gentiles who will inevitably join with remnant Israel to stand before the presence of God. Although the people of Israel expect the salvation of the nation, this messiah brings a salvation from sin, cf. Is.53, Je.31:31-34. He does not restore Israel, but rather restores Israel's relationship with God.
      v22-23. Although the original Hebrew text has "young woman", the Greek LXX uses "virgin" because Isaiah (Is.7:14) is pointing to an amazing sign, the birth of a child deliverer. He will gather his people to God, such that God will be with them (thus the point of the symbolic name "God with us"). We don't know whether Isaiah did actually mean "virgin", but it certainly took on that meaning in time. The birth of Jesus ("All this" refers to the conception and birth, not just the dream of Joseph) fulfills the "Immanuel" prophecy in that Jesus "saves his people from their sins" and so "God is with us" again. Jesus the messiah restores the relationship of broken humanity with God.
      v24-25. So, Joseph marries Mary, but restrains from intercourse with her until after the birth of Jesus. As directed, Joseph names him "Jesus".

Immanuel
      There are many ways of looking at the birth of Jesus, but two, in particular, have vied for our allegiance. There is the incarnational theological view and there is the redemptive theological view.
      In incarnational theology the stress is on God's affirmation of the human condition by his coming to us and his taking upon himself of human flesh. "The 'word became flesh' and elevated the worth of all people because 'God loved the world so much.'" So, the incarnation serves as "God's endorsement of being human". "Christmas is a time to be reminded of our worth in the sight of our Creator."
      Yet, does "'Immanuel', which means, 'God with us'", actually mean that God wants to be with us because he thinks being human is wonderful? Does God, in Christ, take on human flesh to affirm humanity, or does he take on human flesh to save humanity?"
      The Christ-child's real name is "Jesus", which means "he will save". "He will save his people from their sins." In Christ's birth, prophecy is fulfilled. The day dawns when God's people will be "saved", in the sense of saved from their sin and thus reunited to God. It is in this sense that Jesus is "Immanuel". He restores his people to their living God and thus "God is with" them. He restores the relationship of the lost, of the sinner, to their creator God, such that they are with God and God is with them.
      The birth of Jesus is primarily a redemptive act, rather than an incarnational act. Jesus comes to save, and if to save, he must take upon himself human flesh. In our place he becomes the faithful servant of God, even unto death.

v19
      dikaioV adj. "a righteous man" - righteous, just. Joseph was someone who "always did what was right", TEV; "who was a good man", Phillips. Probably a sense such as "compassionate" is better.
      kai "and" - and. Morris argues that the sense is "and yet" because he reads "just" in the sense of someone who obeys the regulations of the law, "and yet did not want ....."
      wn (eimi) pres. part. "because" - The participle of the verb to-be serving to introduce a causal clause.
      mh qelwn (qelw) pres. part. "he did not want" - not wishing. Again the participle serves to form a causal clause.
      deigatisai (deigmatizw) aor. inf. "public disgrace" - to disgrace, shame, expose publicly. The infinitive is complementary, complementing the action of the verb "want", "he was unwilling to bring shame on her", TNT. Joseph did not want Mary shamed publicly. This intention indicates that rather than a "just" man, he was a "compassionate" one.
      laqra/ "quietly" - secretly. Joseph dealt with Mary in-house, "privately", better than "quietly".

v20
      de "but" - Taking an adversative sense.
      enqumhqentoV (enqunomai) aor. part. "after he had considered [this]" - [these things] he was thinking, reflecting. The participle may form a temporal clause as in the NIV, eg. "while/after considering these things", or better, a direct statement expressing a completed action, "he had resolved on this", NEB; "he had made up his mind", Morris.
      kata onar "in a dream" - according to a dream. A term used by Matthew for divine revelations, so possibly just "a word from the Lord was revealed to him in an angelic apparition."
      efanh (fainomai) aor. "appeared" - revealed, showed, appeared
      mh fobhqhV (fobeomai) aor. subj. "do not be afraid" - A negated subjunctive indicating a negative command. "Fear" in the sense of: "do not hesitate", "do not shrink from marrying her."
      paralabein (paralambanw) inf. "to take [Mary] home" - to take home, to lead into one's home. Complementary infinitive, complementing the sense of the verb "afraid". Referring to the marriage custom of a man taking a women into his home as a sign of their union, therefore simply meaning, "to marry."
      gar "because" - for. Causal, serving to establish a logical connection between the two clauses. v21
      texetai (tiktw) fut. "she will give birth" - she will bear.
      kaleseiV (kalew) sing. fut. "you are to give to" - you will call. An imperatival future. Singular = Joseph. "You should give him the name Jesus."
      autoV "he" - Emphatic, "he will save, and no other."
      swsei (swzw) fut. "will save" - "He will rescue, set free", or for the whole clause, "redeem", or "forgive".
      twv aJmartiwn (a) "sins" - The primary meaning of the word is "miss the mark", but came to be used in the LXX and NT for an offence against God, ie. "sin"

v22
      de "-" - but. Note how this particle leads off so many of the verses in this passage. Here it is transitional and not adversative. "Now, ....."
      oJlon (oV) "all" - all, whole, entire, complete.
      gegonen (ginomai) perf. "took place" - happened, occurred.
      iJna + subj. "to [fulfill]" - that. Forming a purpose clause, "these things happened in order to fulfill ....", "so that prophecy would be fulfilled." It is possible that we have here a consecutive clause expressing consequence, result, "these things happened with the consequence that / with the result that prophecy was fulfilled."
      plhrwqh/ (plhrow) aor. subj. "fulfill" - may complete. To realize the promises made by the Lord through the prophets.

v23
      hJ parqenoV (oV) "the virgin" - a young woman who has not had sex. The Greek word may be used of a sexually active young woman, but is normally used of a virgin. On the other hand, the Hebrew word used in Isaiah 7:14 simply means a young woman of marriageable age. None-the-less, it is clear that Isaiah is speaking of a birth which serves as a significant sign to the people, and Matthew reveals the true nature of this sign.
      kalesousin (kalew) sing. fut. "they will call" - Isaiah has the singular "ye will call", indicating Matthew's shift to the fellowship of believers who affirm the name of Jesus.
      meqermhneuomenon (meqermhneuw) part. "means" - having been interpreted, translated.
      meq (meta) + gen. "with" - The sense is either: In Jesus "God is with us", or his name is "God with us.

v24
      egerqeiV (egeirw) pas. part. "when [Joseph] woke up" - rising up, waking up. The NIV takes the participle as temporal, "when/after", best expressed as action completed in time, "on waking from sleep", Moffatt.