Why Christmas carols are so postmillennial

We divide history into BC and AD—Anno Domini, “in the year of the Lord.” But is Christ currently reigning—and if so, why do we mark the beginning of this “year,” this age of Christ, from his birth, rather than his resurrection or ascension? It is because his reign, carried out through his body on earth (his church), is not like the heavy-handed lording of the gentile rulers. It follows the same pattern in the whole world as it does in the life of the individual believer: tender sanctification unto maturity and perfection.