The mystery of Christmas inspired a special kind of quiet exultation four centuries ago in the mind of Spanish composer Tomas Luis de Victoria. It can still be heard in the gentle harmonies of his "Ave Maria," one of the many small masterpieces in the "Christmas With the Folger Consort" program, which will be presented through next weekend at the Folger Shakespeare Library. The calm intensity of this music contrasts curiously with the kinetic exuberance of other Spanish Christmas music from the same period -- for example, the anonymous "Riu, riu, chiu," published during Victoria's childhood, which you cannot hear without wanting to get up and dance.

Some of the best Christmas music was originally written for dancing (the "carol," in fact, was originally a dance form), and this element is vigorously represented in some of the program's numbers, vocal and instrumental. Another aspect of Christmas music in the Middle Ages was its value as a propaganda tool among the still half-pagan peasants of England. "Nowell, nowell . . . be of good cheer and be right merry" meant, among other things, a proclamation that the Christian religion had as much fun to offer as the old beliefs, which attributed mystic qualities to such things as holly and mistletoe. Dancing could not be wiped out (though more than one stern cleric railed against it), so it was baptized.

All these half-forgotten overtones of the ancient feast are embodied in the Folger Consort's program, which is greatly enhanced this year by the presence of the Tallis Scholars, an eight-voice group of English specialists in early music. Some of the music, Spanish and English, is anonymous and deeply rooted in folk styles and traditions. Some is professionally written -- by such composers as Morales, Sweelinck and Praetorius, and particularly an exquisite set by Heinrich Isaac. But still it often draws its inspiration from folk sources. The text often reflects the music's multilevel origins, mingling Latin and vernacular words together just as the music combines dance rhythms with learned polyphony.

Despite its variety of sources, original purposes and styles, the music on this program fits together well. There is a striking contrast between the hard-edged harmonies in the opening group of British carols and the highly polished style of the Isaac group that follows it, but there is also a sense of continuity, of community, of the diverse elements in a complex society joining together to celebrate an event with deep meaning to all.

Vigor and polish, both implicit in the music, are abundantly supplied in the performances. The Tallis Scholars blend their voices not only as skilled specialists but as enthusiasts. The three instrumentalists of the consort, content to support the voices through most of the program, also take some fine moments in the spotlight -- notably in two striking anonymous sets of variations on "Greensleeves."