"Joy to the World" is a popular song frequently sung along with other favorite Christmas songs; however, it is not a Christmas song at all. It is actually a song anticipating the victorious second coming of Jesus Christ instead of His first coming that is celebrated at Christmas.
Have you noticed that nine out of ten people sing the first line incorrectly? Even Mariah Carey sang it wrong in her 1994 edition of "Joy to the World."
The first line is: "Joy to the world: the Lord is come" and not "Joy to the world: the Lord has come" as some people sing.
So, why is the first line "Joy to the world, the Lord is come," rather than "Joy to the world, the Lord has come"?
In the first line, "the Lord has come" might seem more natural, but "the Lord is come" is correct. In Early Modern English, verbs of movement such as "to go" and "to come" were used with the auxiliary verb "to be" and not the present-day auxiliary verb "to have."
The phrase "the Lord is come" uses an archaic form of English that was very common in 1719 when “Joy to the World” was written by Isaac Watts based on Psalm 98. A number of references say that this construction uses the word come as an unaccusative intransitive verb.
An unaccusative verb is an intransitive verb whose subject does not actively initiate, or is not actively responsible for, the action of the verb.
Basically, to say "the Lord is come" puts the emphasis on the state of having come and now being here, as opposed to saying, "the Lord has come," which simply puts the emphasis on the action of coming. The Lord didn't just come, He is here now.
To say that "The Lord is come," is not only to emphasize that He is here, but it also demonstrates that the subject, the Lord, did not actively initiate the coming Himself. To say, "The Lord has come," puts the emphasis on the action of coming, and implies that the Lord is the one who initiated the coming. That's why we should not sing, "The Lord has come."
But to say, "The Lord is come," puts the emphasis on the fact that He is now here, and implies that the Lord is not the one who initiated this coming, but that he was sent by the Father according to John 3:16.
Based on this, the next time you sing "Joy to the World," be mindful to say "the Lord is come."