Many are quite good—there’s no need to mention them. But some are quite misleading, if not heretical. This is just a warning, and a call to urge you to examine what you are singing!
Consider this: In It Came Upon the Midnight Clear you sing that the angels touched the earth with their harps of gold. Who says so? And you end the carol by informing the world that “with the ever-circling years?” an age of gold will “come round” once again. That’s a sample of Greek cyclical philosophy of time—Christian theology holds to linear thinking: beginning, middle, end.
How about Oh Holy Night? First, there is nothing about the night that makes it holy, or, as the carol goes on to call is “a night divine. Let’s sing about the Savior—night the night of His birth!
Just those two songs for now. The goal is to jar you a bit into thinking about what you singing. Be sure it is biblical. That’s the point. Hymns, songs, carols serve two purposes: 1. to praise God, 2. to witness to His truth. Be sure when you sing you do so.