Saints, before the altar bending,
Watching long in hope and fear;
Suddenly the Lord, descending,
In His temple shall appear.
(James Montgomery, Angels From The Realms Of Glory)
"the Lord, whom you seek, will suddenly come to His temple" (Malachi 3:1)
We often underestimate something once we're accustomed to it. Every year at Christmas, billions of people celebrate the incarnation, some more intentionally than others. Many leaders of Gentile nations profess allegiance to Jesus Christ (Isaiah 52:15), a remarkable fact in light of Christianity's origins. N.T. Wright comments that “no second-Temple Jews known to us were expecting the one god to appear in human form” (The Resurrection Of The Son Of God [Minneapolis, Minnesota: Fortress Press, 2003], p. 573). The early Christians were often criticized for their belief in the incarnation:
"This assertion [the incarnation], says Celsus, 'is most shameful and no lengthy argument is required to refute it' (c. Cels. 4.2). God is not the kind of being who can undergo mutation or alteration. He cannot change from the purity and perfection of divinity to the blemished and tarnished state of humans." (Robert Wilken, The Christians As The Romans Saw Them [New Haven and London: Yale University Press, 1984], p. 102)
Despite a lack of Jewish expectation at the time of early Christianity, some passages in the Old Testament do anticipate the incarnation. And now billions of Gentiles celebrate the event. God's promise of blessing the world through Abraham (Genesis 12:2-3) is being fulfilled spectacularly. We often focus on fulfilled prophecies like Jesus' Davidic ancestry and His birth in Bethlehem, largely because those prophecies are so specific. But as vague as God's promise to Abraham was, its fulfillment is wonderfully impressive.
From a worldly perspective, the most powerful man on earth at the time of Jesus' birth was the Roman emperor Augustus. He didn't think much of the Jewish people or their Messianic hopes. Like other politicians, he would sometimes cooperate with the Jewish people or pay homage to the Jewish deity as one god among others, but "he revered the ancient and approved [foreign cults], like the mysteries of Eleusis in Attica, but despised the rest, taking no notice in Egypt of the bull-cult of Apis, and congratulating his grandson for passing by the temple in Jerusalem" (Andrew Wallace-Hadrill, Suetonius [London, England: Bristol Classical Press, 2004], pp. 189-190)
Augustus was emperor during both Jesus' presentation in the temple (Luke 2:22-38) and His later visit at the age of twelve (Luke 2:46-50). While Augustus thought little of the Jewish temple and encouraged his grandson in avoiding it, God visited that temple and established a kingdom that would overcome and far exceed the kingdom of Augustus.
"When 'the fulness of the time' was come, God sent forth his only-begotten Son, 'the Desire of all nations,' to redeem the world from the curse of sin, and to establish an everlasting kingdom of truth, love, and peace for all who should believe on his name....There is no conflict between the historical Jesus of Nazareth and the ideal Christ of faith. The full understanding of his truly human life, by its very perfection and elevation above all other men before and after him, will necessarily lead to an admission of his own testimony concerning his divinity. 'Deep strike thy roots, O heavenly Vine, Within our earthly sod! Most human and yet most divine, The flower of man and God!' Jesus Christ came into the world under Caesar Augustus, the first Roman emperor, before the death of king Herod the Great, four years before the traditional date of our Dionysian aera. He was born at Bethlehem of Judaea, in the royal line of David, from Mary, 'the wedded Maid and Virgin Mother.' The world was at peace, and the gates of Janus were closed for only the second time in the history of Rome. There is a poetic and moral fitness in this coincidence: it secured a hearing for the gentle message of peace which might have been drowned in the passions of war and the clamor of arms. Angels from heaven proclaimed the good tidings of his birth with songs of praise; Jewish shepherds from the neighboring fields, and heathen sages from the far east greeted the newborn king and Saviour with the homage of believing hearts. Heaven and earth gathered in joyful adoration around the Christ-child, and the blessing of this event is renewed from year to year among high and low, rich and poor, old and young, throughout the civilized world." (Philip Schaff, History Of The Christian Church, 1:2:15)