Sometimes a song's chorus becomes popular in itself. That is true of the chorus of "O Come All Ye Faithful." I have heard the chorus sung with added words:

Oh, come let us adore Him.

We'll give Him all the glory.

For He alone is worthy.

"O Come All Ye Faithful" was originally written in Latin as "Adeste Fidelis."  "Adeste Fidelis" literally means "be present, or near, ye faithful."

John Wade, an English layman is believed either to have written it or copied it in the 1700's.  There is a second stanza that is usually omitted.  It is:

God of God and Light of Light begotten, Lo, He abhors not the Virgin's womb:

Very God begotten, not created--O come, let us adore Himl.

Later, in the 1800's, an Anglican minister, Frederick Oakeley translated it into the English form we know today.

This video was made for the deaf.