Matthew 1:20-21 But when he had considered this, behold, an angel of the Lord appeared to him in a dream, saying, “Joseph, son of David, do not be afraid to take Mary as your wife; for the Child who has been conceived in her is of the Holy Spirit. 21 She will bear a Son; and you shall call His name Jesus, for He will save His people from their sins.”
Much like we see Gabriel doing for Joseph in Matthew 1:20-23 and then Mary in Luke 1:26-38, the ability to grab hold of Christ and His mission is increased as a result of angelic assistance. Mary and Joseph were both believers in the promises of God who already were operating in dependence upon the grace of the Spirit working on and upon them. However they needed the ability to grasp the unusual and miraculous nature of what God in the Person of the Son was undertaking. Angels have been used by God to aid in both the communication of His word, its explanation, and protection of those receiving it. However this particular bit of good news required ample aid by angels. The Christmas accounts reveal to us just how zealous the angels are over the glory of Christ and the need for His people to share in that zeal.
So we see angels pronouncing Christ's main mission for coming to earth, but notice what they also pronounced in the Christmas accounts of Matthew and Luke...
Angels pronounced Christ's majesty
Luke's Gospel in particular records how the Angels served to point God's people to the majesty of the Son in the following ways:
a. The Davidic Covenant. Luke 1:32 "throne of His father David" cf 2 Samuel 7:13-16
b. The Abrahamic Covenant. Luke 1:33 "house of Jacob forever" cf Genesis 12:1-7
c. The New Covenant. Luke 1:33 "kingdom will have no end" cf Isaiah 9:6-7; Jeremiah 31:31-34
The second significance of the virgin birth has to do with Christ in his humanity fulfilling the scriptures that detail the virgin birth. (Isaiah 7:14) The angelic involvement in expressing this truth to people like Joseph, Mary, the Shepherds and to us was so that we could behold the majesty of Christ in scripture and His humanity. But notice a final point the angels communicated about Christ's majesty...
When God utilized "signs" in the Bible, the sign was meant to "signify" a major reality or event or more so, God Himself showing up at that event. So the question is: what is the significance of the sign of the baby in the manger? The Angels proclaim in Luke 2:13-14 "And suddenly there appeared with the angel a multitude of the heavenly host praising God and saying,“Glory to God in the highest,
and on earth peace among men with whom He is pleased.” The babe in the cradle never ceased being God in the highest! That is the point of the angelic proclamation!