This is how the birth of Jesus Christ came about.
When his mother Mary was betrothed to Joseph,
but before they lived together,
she was found with child through the Holy Spirit.
Joseph her husband, since he was a righteous man,
yet unwilling to expose her to shame,
decided to divorce her quietly.
Such was his intention when, behold,
the angel of the Lord appeared to him in a dream and said,
“Joseph, son of David,
do not be afraid to take Mary your wife into your home.
For it is through the Holy Spirit
that this child has been conceived in her.
She will bear a son and you are to name him Jesus,
because he will save his people from their sins.”
All this took place to fulfill what the Lord had said through the prophet:
Behold, the virgin shall conceive and bear a son,
and they shall name him Emmanuel,
which means “God is with us.”
When Joseph awoke,
he did as the angel of the Lord had commanded him
and took his wife into his home.
The virginal conception of Jesus is the work of the Spirit of God. Joseph’s decision to divorce Mary is overcome by the heavenly command that he take her into his home and accept the child as his own. The natural genealogical line is broken but the promises to David are fulfilled; through Joseph’s adoption the child belongs to the family of David. Matthew sees the virginal conception as the fulfillment of Is 7:14.
1:18 Betrothed to Joseph: betrothal was the first part of the marriage, constituting a man and woman as husband and wife. The betrothal was followed some months later by the husband’s taking his wife into his home, at which time normal married life began.
1:19 A righteous man: as a devout observer of the Mosaic law, Joseph wished to break his union with someone whom he suspected of gross violation of the law. It is commonly said that the law required him to do so, but the texts usually given in support of that view, e.g., Dt 22:20–21 do not clearly pertain to Joseph’s situation. Unwilling to expose her to shame: the penalty for proved adultery was death by stoning; cf. Dt 22:21–23.
1:20 The angel of the Lord: in the Old Testament a common designation of God in communication with a human being. In a dream: see Mt 2:13, 19, 22. These dreams may be meant to recall the dreams of Joseph, son of Jacob the patriarch (Gn 37:5–41:19).
1:21 Jesus: in first-century Judaism the Hebrew name Joshua (Greek Iēsous) meaning “Yahweh helps” was interpreted as “Yahweh saves.”
1:23 God is with us: God’s promise of deliverance to Judah in Isaiah’s time is seen by Matthew as fulfilled in the birth of Jesus, in whom God is with his people.
Friends, today’s Gospel centers on the intriguing figure of Joseph. Joseph is one of the most beloved of the saints, featured in countless works of art and prominent in the devotional lives of many. We know almost nothing about him, yet some very powerful spiritual themes emerge in the accounts of Joseph. He had become betrothed to Mary and this union had been blessed by God. And then he finds that his betrothed is pregnant.
This must have been an emotional maelstrom for him. And at a deeper level, it is a spiritual crisis. What does God want him to do? Then the angel appears to him in a dream and tells him, “Joseph, son of David, do not be afraid to take Mary your wife into your home.” He realizes at that moment that these puzzling events are part of a much greater plan of God’s. What appears to be a disaster from his perspective is meaningful from God’s perspective.
Joseph was willing to cooperate with the divine plan, though he in no way knew its contours or deepest purpose. Like Mary at the annunciation, he trusted and let himself be led.
– Robert Barron
May the virtues of faith, hope, and love go with you today – DV.
 Donald Senior, John J. Collins, and Mary Ann Getty, eds., The Catholic Study Bible, 2nd Ed.: Notes, 2nd ed., vol. 2 (New York: Oxford University Press, 2011), 1337–1338.