This was the first song I heard from Steeleye Span. A keyboardist we tried to fit with in college, Bobby McConnahay, worked at a record store and told me to come by to listen to something. He knew his mark. I listened and was entranced. I loved the implied sound in the "Below the Salt" recording, of the monks processing in, singing the central verses, and then out again.
Ch: Gaudete, gaudete, Christus est natus Ex Maria virgine, gaudete Gaudete, gaudete, Christus est natus Ex Maria virgine, gaudete Tempus adest gratiae, hoc quod optabamus Carmina laetitiae devote redamus Deus homo factus est natura mirante Mundus renovatus est a Christo regnante Ezechielis porta clausa per transitur Unde lux est orta salus invenitur Ergo nostra cantio psallat iam in lustro Benedicat domino salus regi nostro
The chorus is Rejoice, rejoice, Christ is born of the Virgin, Mary.
Notice the similarity of "Gaudete," rejoice, and our word "gaudy."
Same root, and worth considering if you want to really rejoice.
It is 16th C or earlier, from a collection of Scandinavian carols