Christmas songs, or carols, are usually relegated to be sung once a year -- at least by "Christmas traditionalists". OTOH, some folks may wish they were never sung at all!
If these songs contain truths about Jesus and His birth, why shouldn't they be sung? If these songs contain truths based on the holy Scriptures, why shouldn't they be sung year around? If they're not fit sing year around, should we sing them at all?
Some "Christmas traditionalists", if they hear "Joy to the World" sung in the summer, react as if someone has broken some sacred unwritten law! This song is among my favorites. I think it should/could be sung whenever the Spirit moves.
Joy to the world, the Lord is come!
Let earth receive her King;
Let every heart prepare Him room,
And Heaven and nature sing.
Joy to the earth, the Savior reigns!
Let men their songs employ;
While fields and floods, rocks, hills and plains
Repeat the sounding joy.
No more let sins and sorrows grow,
Nor thorns infest the ground;
He comes to make His blessings flow
Far as the curse is found.
He rules the world with truth and grace,
And makes the nations prove
The glories of His righteousness,
And wonders of His love.
-- Isaac Watts, 1719