John Piper:

And so the “us” of “O come let us adore him” is the “us” of heaven and earth, singing together. According to Revelation 9:16, there are at least 200 million angels at God’s bidding. Surely at least some of them are assigned to give heed to us as we sing, and do what we say: “Sing choirs of angels, sing in exultation!” If we could only hear! Heaven and earth married in singing to Christ.

The choir of men and angels join together in song to worship the creator of the universe, who came to rescue and restore the human race from our own brokenness.

I love this dissection of such a beautiful and rich hymn. Christmas is about so much more than just a cute little baby Jesus in the manger.