The announcements of the conception and of the birth of Jesus make known or reveal who Jesus is in Heaven. As such, to secure our salvation, His church, His flock also confesses with our mouth that Jesus is YHWH, the I AM. Luke 1:31, 2:11; Matthew 1:18-21, John 8:24, Romans 10:9-11.

1. YEHOSHUA was announced as Savior of HIS people, that is, as YAHWEH God who owns the Jews

Matthew 1:18-21 ASV
(18)  Now the birth of Jesus Christ was on this wise: When his mother Mary had been betrothed to Joseph, before they came together she was found with child of the Holy Spirit.
(19)  And Joseph her husband, being a righteous man, and not willing to make her a public example, was minded to put her away privily.
(20)  But when he thought on these things, behold, an angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Spirit.
(21)  And she shall bring forth a son; and thou shalt call his name JESUS; for it is he that shall save his people from their sins.

2. Messenger of YAHWEH announced the birth of YEHOSHUA | JESUS as the birth of MESSIAH YAHWEH not as 

Luke 2:8-21 ASV
(8)  And there were shepherds in the same country abiding in the field, and keeping watch by night over their flock.
(9)  And an angel of the Lord stood by them, and the glory of the Lord shone round about them: and they were sore afraid.
(10)  And the angel said unto them, Be not afraid; for behold, I bring you good tidings of great joy which shall be to all the people:
(11)  for there is born to you this day in the city of David a Saviour, who is Christ the Lord.
(12)  And this is the sign unto you: Ye shall find a babe wrapped in swaddling clothes, and lying in a manger.
(13)  And suddenly there was with the angel a multitude of the heavenly host praising God, and saying,
(14)  Glory to God in the highest, And on earth peace among men in whom he is well pleased.
(15)  And it came to pass, when the angels went away from them into heaven, the shepherds said one to another, Let us now go even unto Bethlehem, and see this thing that is come to pass, which the Lord hath made known unto us.
(16)  And they came with haste, and found both Mary and Joseph, and the babe lying in the manger.
(17)  And when they saw it, they made known concerning the saying which was spoken to them about this child.
(18)  And all that heard it wondered at the things which were spoken unto them by the shepherds.
(19)  But Mary kept all these sayings, pondering them in her heart.
(20)  And the shepherds returned, glorifying and praising God for all the things that they had heard and seen, even as it was spoken unto them.
(21)  And when eight days were fulfilled for circumcising him, his name was called JESUS, which was so called by the angel before he was conceived in the womb.