God Rest Ye, Merry, Gentlemen

When I was younger, I misunderstood this Christmas hymn. In my mind, I ignored the second comma in the title. So, I thought the song was speaking to "merry gentlemen." "Merry" is not an adjective describing the gentlemen. Rather, "merry" refers to the blessing brought on gentlemen (and gentlewomen) and is the opposite of "dismay" in the second line. The transitive use of the verb rest in the sense "to keep, cause to continue, to remain" is typical of 16th- to 17th-century language.

The historic meaning of the phrase is something like "May God give you peace and keep you in a state of good cheer" because "Christ our Savior was born on Christmas Day!"