A verse that has never ceased to make me awe in wonder is Galatians 4:4, "In the fullness of time God sent forth his son, born of a woman, born under the law". I have found this to be among the most under appreciated verses in the entirety of the New Testament. This verse, among others, casts the person and work of Christ in view of the entire history of God's dealings with his people. A history that finds its fullness in Christ. A providential history that is evidenced by a bright star.
The Fullness of "Time"
The significance of there being a "fullness of time" is often quite minimized. Some will speak of the fullness being merely of a geopolitical nature with respect to the Roman Empire. Others will speak of the fullness being a cultural dynamic with respect to the wide-reaching Greek language and its precise character. Both of these were certainly established in God's providence to serve the purpose of his Son coming into our world. But what if this fullness of time means something even greater?
Perhaps the key aspect to discovering the trajectory of Gal 4:4 is to recognize the presence of the word "time" (χρόνος). It is time itself that is in its fullness. But what does it mean for time itself to be full? To understand this we must be aware of what Paul is establishing in this section of Galatians. Since Gal 3:15 he has been presenting that the history of God's people is a covenantal history. His overall point in this section is to demonstrate that a person is saved not by their own works of the law but by faith in Jesus Christ. He does this by showing that the law (which is housed in a covenantal format) was by its very nature instituted for the sake of displaying the forthcoming "offspring"; Jesus Christ (Gal 3:16, 3:25). The law was never intended to "supply life" but to prepare for the promised redeemer (Gal 3:21, cf. Gen 3:15).
Paul will go on to argue how this doesn't allow for licentious living but for now he is walking us through the covenant history of God's people and displaying how it is a redemptive history which finds its most full expression in the person and work of Jesus Christ. "Time" in Paul's argument is with respect to the history of redemption. Richard B. Gaffin agrees when he writes in his work In the Fullness of Time,
"In view globally, when we speak of redemptive history, is the history that begins in the garden following the fall and the resulting curse on human sin that affects the entire creation (Rom. 8:20‒22), largely incorporating in its unfolding the history of Israel, and reaches its consummation in the work of Christ in 'the fullness of time' (Gal. 4:4), when “the Word became flesh and dwelt among us” (John 1:14)."
Revelation is a historical process that finds its climactic expression in Jesus Christ (Heb 1:1-2). It is this framework that Paul has in mind when he says there is a fullness of "time". "Time" in Gal 4:4 is the history of God's dealings with his covenant people (which the Hebrews text understands as corresponding with God's special revelation; "word-deed revelation") which is inherently redemptive in nature. It is because this redemptive history finds its climactic expression in the person and work of Jesus Christ that Paul can understand this time to have reached its fullness when Christ comes "born of a woman, born under the law". But what does this have to do with the star of Bethlehem?
The Fullness of General Revelation
When we speak of redemptive history we are speaking strictly in terms of God's providential acts with his covenant people and the special revelation that corresponds with them. We are not, however, referring to general revelation. And yet, I want to ask this question: If all of special revelation hinges on the person and work of Christ, what might that mean for general revelation? Though our ability to speak about general revelation is much less than our ability to speak about special revelation (we should be hesitant to speak dogmatically about general revelation insights). The Bible does offer us helpful categories for interpreting general revelation especially with stars.
The purpose of the stars is presented right in Genesis 1:14 when it refers to the stars being created "for signs and for seasons". They are communicative in nature and that's why Jesus refers to the stars being the communicators for when he is returning in glory (Luke 21:25). The stars we set up to communicate seasons. Or, to speak in redemptive-historical categories, the stars were arranged by God to communicate the changing epochs of redemptive history. They will communicate when Christ comes again (Luke 21:25) and they communicated when Christ came on that first Christmas morning (Matt 2:2, cf. 9-10). The wise men of Matthew 2 "saw his star when it rose and [came] to worship him."
Many (including myself for a very long time) assumed that this star was just painted by God when Christ was born. But the Bible tells a very different story.
These stars were set by God from the very beginning to be signs. Thus, the star of Bethlehem had been coursed in Genesis 1 to show itself as sign for when the Christ would come. The star over Bethlehem displays for us, just as Gal 4:4 and Heb 1:2 declare, that the fullness of time is defined by the person and work of Jesus Christ who was born of a woman, born under the law.