Charles Wesley wrote Hark! The Herald Angels Sing in 1739. The hymn borrows its tune from Mendelssohn and its lyrics from Wesley's meditation on the incarnation. The opening line hark frames the entire hymn as an announcement: something has happened that heaven itself cannot stay silent about.
Wesley understood that the incarnation is not about sentiment but about reversal. God comes down, not to be coddled, but to be resisted and killed. The hymn doesn't hide this: Christ is born to raise the sons of Earth, Christ is born to give them second birth. The manger holds the Savior of the world.
The theological claim is staggering: Veiled in flesh the Godhead see, Hail the incarnate Deity. How can divinity veil itself in human flesh? Only by infinite condescension. Yet the hymn sings this not as tragedy but as triumph. God became human so that humans might become capable of bearing God's glory.