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 be with child and bear a son, and they shall name him Emmanuel, which means "God is with us." (Mt 1:1-25)
https://bible.usccb.org/bible/readings/121823.cfm
“Do not be afraid.” In the encounter with God we need to hear these words, because like Moses, we are standing on Holy Ground. O Mighty Lord, and leader of the house of Israël, who appeared to Moses in the burning bush, and on Sinai gave him the law, come to redeem us with outstretched arm.