Christmastime means “Messiah” time, but there are many other pieces to sing, not the least of which is the Christmas oratorio by Handel’s exact contemporary, Johann Sebastian Bach. And on Sunday afternoon, this oratorio was heard at St. Bartholomew’s Church – or rather, Parts I through III were heard; Parts IV through VI can be heard on January 2.Think of it as a musical cliffhanger.

The oratorio is being performed under the rubric of “Cantatas in Context,” a project of Bach scholar Mary Greer. As a program note put it, this series “offers a deeper appreciation of Bach’s sacred works by organizing the programs around the concept of the liturgical year, which was integral to Bach’s conception of [his] cantatas.” It is a good idea. Ms. Greer served as conductor on Sunday afternoon; her forces were the New York Baroque Soloists and the Orchestra of St. Luke’s.

Conductor and singers walked out to no applause, which was a little strange; perhaps people felt they should behave as though at a church service. Then Ms. Greer, microphone in hand, said she wanted to say something about the Christmas Oratorio. Uh-oh. For me, the most dread (hyphenated) word in the English language is concert-lecture. For about 15 minutes, Ms. Greer lectured about the work, having the orchestra provide musical examples. What she had to say was utterly sound, no doubt – but, in my view, nothing kills the spirit of Christmas (or the Christmas Oratorio) like a lecture. It also raised a question: Would Ms. Greer conduct like an academic?

The opening piece was not encouraging: That was “Jauchzet, frohlocket,” a chorus that is one of the most glorious things ever written. The orchestra played in its “period” style, with lightness and bounce. But they were not together, and they were not convincing. On the positive side, the trumpeter was superb. The singers did better than the orchestra, although the men were off pitch (flat). Ms. Greer conducted in a stately, placid, rather phlegmatic way. The results were unrousing, to put it mildly. And, in this piece, it’s quite nice to let the timpani out. Who, who, who will let the timpani out?

When “Jauchzet, frohlocket” ended, I thought of a favorite story. Years ago, my fellow critic Fred Kirshnit was taken to “The Flying Dutchman” at the Metropolitan Opera by his uncle Syd. At the conclusion of the overture, Uncle Syd leaned over to Fred and said, “It’s all downhill from here, kid.”

Well, the Christmas Oratorio offers glorious music throughout, but little can be as thrilling as that opening chorus.

The tenor in the role of the Evangelist was William Ferguson, and he sang a clean German, although he sang some unfortunate – some wrong – notes. Soon enough, however, we got Brenda Patterson, the mezzo-soprano of the afternoon. What a revelation. Her instrument is juicy and beautiful, and her technique is rock-solid: She sings in the center of the center of any note. And she sings with taste, style, and intelligence. One had the impression of listening to – of discovering, in my case – a great singer. If there’s any justice, she will be rich and famous.

But then came a chorale. You could call it intimate and personal; or you could call it wrongly retiring. It was, in fact, flaccid and soupy, in need of some spine, some assertiveness, some up-and-down Lutheranness. And in an ensuing chorale and recitative, it was as though the singers were scared to sing – would they waken someone?

Then, however, came the afternoon’s bass soloist, who was Christopheren Nomura, showing off a beautiful, resonant instrument, which he knows how to use. You might have asked for more “give” in certain passages – he was a bit stentorian – but this was obviously a first-rate singer.

Part I concluded with another sickly chorale, although that trumpeter broke through the gloom.

Part II began with a … well, sickly Sinfonia, followed shortly by still another chorale of the same nature. An inexplicable wanness took over. I was reminded of the concert that the Choir of King’s College, Cambridge, gave at St. Ignatius Loyola Church last week, so somber, even grim. Don’t they know it’s Christmas? Bach has not written dirges here.

The tenor aria “Frohe Hirten” is one of the sprightliest, most joyful, and most interesting of all Bach arias. You would never have known it. As presented at St. Bart’s, it was slow and ponderous. The soloist, Benjamin Sosland, is clearly capable, and so is the flutist who played with him; but this rendition did not show them to best effect.

Ms. Patterson came up again in the great aria “Schlafe, mein Liebster,” in which the orchestra began very slowly and very sloppily – that is a bad combination, as you can imagine. Not even this singer could defeat the monotony of this effort.

Mary Greer is unquestionably an authority on Bach, with loads to offer. But not everyone is born to be a conductor. And let me repeat one of my bromides: One of the joys of concert going is that you never know what you’re going to get. One Sunday afternoon, you go to a church to hear a sleepy little performance of the Christmas Oratorio, and you encounter a great singer: Brenda Patterson.

“Christmas Oratorio, Parts IV-VI” will be performed January 2 at 3 p.m. (109 E. 50th Street, at Park Avenue 212-378-0200).