One of my favorite carols is Joy To The World. The words are by Issac Watts, based on Psalm 98: "Make a joyful noise unto the Lord, all the earth; make a loud noise, and rejoice, and sing praise. Let the floods clap their hands; let the hills be joyful together before the Lord; for He cometh to judge the earth, with righteousness shall he judge the world, and the people with equity."
Some say Joy To The World is not about the birth of Christ in Bethlehem. They say it is about His second coming, not His first. (See http://en.wikipedia.org/wiki/Joy_to_the_World.)
The joy that is sung about, then, is a future joy that will occur when Christ returns, to “make the nations prove the glories of His righteousness,” in that full expression of His Kingdom (yet-to-come).
But for me, the song also makes sense as a celebration of the first coming of Christ in Bethlehem. While I’m looking forward to that full and perfect expression of Christ’s Kingdom-yet-to-come, I’m also celebrating the Kingdom-already-here. Jesus is Lord of all. Today! Not just in the future, but in this present moment (Acts 10:36-37)!
The Lord is come! No, the Kingdom of God isn't fully recognized yet, or perfectly functional right now. This will happen when Christ comes the second time. But the domain over which Christ is King (that is, His King-domain) presently includes both Heaven and Earth.
This is the greatest Christmas gift: Christ the King has come to Earth “to make His blessings flow, far as the curse is found, far as the curse is found.” Right now. Our Savior has come to make His blessings flow through people who are reconciled to God, and reconciling all things around them to Him, including the things of Earth. That's the big idea behind Christ's coming in the first place. See Col. 1:16-20, and To Reconcile Not Only People But Things.
So, no more let thorns infest the ground. By God's amazing grace, let's put our work gloves on, go to our workplaces after the Christmas holiday, both at home and in the community, to pull up bramble bushes─and plant redwood trees.
Joy to the Earth! the Savior reigns; Let men their songs employ; While fields and floods, rocks, hills, and plains, Repeat the sounding joy, Repeat the sounding joy, Repeat, repeat the sounding joy!
Far as the curse is found.