“And you, who once were alienated and hostile in mind, doing evil deeds, he has now reconciled in his body of flesh by his death, in order to present you holy and blameless and above reproach before him, if indeed you continue in the faith, stable and steadfast, not shifting from the hope of the gospel that you heard, which has been proclaimed in all creation under heaven, and of which I, Paul, became a minister.” (Colossians 1:21–23, ESV)
There is a slightly carnal side of me that enjoys the fact that every time an unbeliever or an atheist dates and signs a check or another official document they are having to give credence to the fact that over two thousand years ago something dramatic happened that ultimately changed the way the world keeps track of time. On archaeological signs in Israel you will find dating as BCE or ACE. BCE means “before the common era,” and ACE means “after the common era.” Sometimes just CE is used for the “common era.” These are nonreligious designations since to use BC (before Christ) or AD (Anno Domini, the year of our Lord) would link the dating to what really changed the world—the incarnation of Jesus Christ, the Son of God who really is the Lord. Those who don’t believe Jesus is Messiah and Lord just don’t want to go there. Ironically, the dates are all the same regardless of the designation one uses. Hence it really is Jesus who defines the eras.
At a more personal level, Paul in Colossians 1:21–23 shows the change Jesus brings into our lives as he describes what life is like before and after Christ changes our birthday spiritually.
Without the incarnation there could be no death and resurrection—hence no good news as to how we who were born into this world with a nature tainted by alienation, hostility, and evil behavior could be reconciled, declared righteous, and one day, stand before Him in holiness. All of this happens as a result of our second birthday, our spiritual birthday when we trusted Christ by faith. The connections between gospel proclamation, personal faith, steadfast living, and hope are held together because of what happened as a result of that first Christmas.