Bach's Christmas Oratorio, BWV 248, consists of a set of six cantatas, each with recitatives, arias, and chorales. Moreover, some of the music for this most solemn of Christian events was borrowed by Bach from his own secular compositions. Yet it is a unified work, designated by Bach himself as an oratorio, and the biblical narration of the Christmas story is worked into the usual recitative-aria structure. There aren't any melodies in the work that are really among Bach's greatest hits, but the ingenuity of the work as a whole lies in the way it's somehow greater than the sum of its parts. That's the appeal of this version by conductor Stephen Layton, four of his favored soloists, the Choir of Trinity College, and the period-instrument Orchestra of the Age of Enlightenment: it respects the small scale of the parts but treats the whole with the weight it deserves. Credit for the balance must go to Layton, who has gotten splendid results from the youthful Cambridge choristers in a variety of common repertory works. They enunciate clearly, hit the pitches precisely, and generally seem excited by what they're doing. The always lively Orchestra of the Age of Enlightenment is a perfect partner for the choir, and the soloists engage with the text and convey the feeling that they're in the ballpark of the ones who originally performed the work. There are more daring performances of the Christmas Oratorio on all fronts, but few that make such a satisfying and musical impression.