1. Our invisible God made Himself visible to His own people

"He is the image of the invisible God, the firstborn over all creation. For by Him all things were created that are in heaven and that are on earth, visible and invisible, whether thrones or dominions or principalities or powers. All things were created through Him and for Him." Colossians 1:15-16

 

"...hidden in God who created all things through Jesus Christ; to the intent that now the manifold wisdom of God might be made known by the church to the principalities and powers in the heavenly places, according to the eternal purpose which He accomplished in Christ Jesus our Lord." Ephesians 3:9-11

2. Revelation to a select few

 

Only a few lowly shepherds saw the angels and heard the message. Were there other shepherds in the field who were not privileged to see and hear? Probably. And no one else in Bethlehem (which was crowded because of the census) were invited to the heavenly feast.

"Now there were in the same country shepherds living out in the fields, keeping watch over their flock by night. And behold, an angel of the Lord stood before them, and the glory of the Lord shone around them, and they were greatly afraid. Then the angel said to them, '

"Do not be afraid, for behold, I bring you good tidings of great joy which will be to all people. For there is born to you this day in the city of David a Savior, who is Christ the Lord. And this will be the sign to you: You will find a Babe wrapped in swaddling cloths, lying in a manger.”

"And suddenly there was with the angel a multitude of the heavenly host praising God and saying:  'Glory to God in the highest, and on earth peace, goodwill toward men!”' Luke 2:8-14

3. An Old Testament example

 

A large army of God's victorious angels were made visible to Elisha and his servant during a tumultuous time. God opened their eyes, and they saw what no one else could see:

"Now the king of Syria was making war against Israel; and he consulted with his servants, saying, 'My camp will be in such and such a place.” And the man of God [Elisha] sent to the king of Israel, saying, 'Beware that you do not pass this place, for the Syrians are coming down there.' Then the king of Israel sent someone to the place of which the man of God had told him. Thus he warned him, and he was watchful there....

"... the heart of the king of Syria was greatly troubled by this thing [he feared there might be a spy in his midst]; and he called his servants and said to them, 'Will you not show me which of us is for the king of Israel?”

"And one of his servants said, 'None, my lord, O king; but Elisha, the prophet who is in Israel, tells the king of Israel the words that you speak in your bedroom.' So he said, 'Go and see where he is, that I may send and get him.' And it was told him... 'Surely he is in Dothan.' Therefore he [the Syrian king] sent horses and chariots and a great army there, and they came by night and surrounded the city. And when the servant of the man of God arose early and went out, there was an army, surrounding the city with horses and chariots. And his servant said to him, 'Alas, my master! What shall we do?'”

 So he [Elisha] answered, 'Do not fear, for those who are with us are more than those who are with them.' And Elisha prayed, and said, 'Lord, I pray, open his eyes that he may see.'

"Then the Lord opened the eyes of the young man, and he saw. And behold, the mountain was full of horses and chariots of fire all around Elisha." 2 Kings 6:8-17

3. The birth of Jesus is central to God's unfolding, eternal plan.

"...another sign appeared in heaven: behold, a great, fiery red dragon having seven heads and ten horns....  And the dragon stood before the woman who was ready to give birth, to devour her Child as soon as it was born. She bore a male Child who was to rule all nations with a rod of iron. And her Child was caught up to God and His throne. Then the woman fled into the wilderness, where she has a place prepared by God..." Revelation 12:3-6

To understand the dragon's assault and the mortal danger to Jesus, ponder the next passage. Remember, Herod was an intensely paranoid, brutal and murderous ruler. Fearing competition and rebellion from his family as well as court, he assassinated several wives and many of his sons. Here is an earthly and finite view of the spiritual battle glimpsed in the last quote: 

"Now after Jesus was born in Bethlehem of Judea in the days of Herod the king, behold, wise men from the East came to Jerusalem, saying, 'Where is He who has been born King of the Jews? For we have seen His star in the East and have come to worship Him.'

"When Herod the king heard this, he was troubled, and all Jerusalem with him. And when he had gathered all the chief priests and scribes of the people together, he inquired of them where the Christ was to be born. So they said to him, 'In Bethlehem of Judea, for thus it is written by the prophet:

    "But you, Bethlehem, in the land of Judah, are not the least among the rulers of Judah;
      For out of you shall come a Ruler Who will shepherd My people Israel. ”

"Then Herod, when he had secretly called the wise men, determined from them what time the star appeared. And he sent them to Bethlehem and said,

"Go and search carefully for the young Child, and when you have found Him, bring back word to me, that I may come and worship Him also.”

"When they heard the king, they departed; and behold, the star which they had seen in the East went before them, till it came and stood over where the young Child was. When they saw the star, they rejoiced with exceedingly great joy. And when they had come into the house, they saw the young Child with Mary His mother, and fell down and worshiped Him. And when they had opened their treasures, they presented gifts to Him: gold, frankincense, and myrrh.
 

"Then, being divinely warned in a dream that they should not return to Herod, they departed for their own country another way." Matthew 2:1-12