The Mostly Mozart Festival is over, ending not so strong as it began, a month ago. On Thursday night, the Russian Patriarchate Choir gave a concert in Alice Tully Hall. And on Saturday night, in Avery Fisher Hall, that choir joined the Concert Chorale of New York and the Mostly Mozart Festival Orchestra for Mozart’s C-minor Mass. That was the grand finale.

But first to the Russian evening, in Alice Tully.

One of the fruits of the Soviet Union’s collapse was the reemergence of Russian choral music, so much of which is liturgical. The Russian Patriarchate Choir was founded by Anatoly Grindenko in 1983. This was several years before the Soviet Union fell, and the group had to be cautious for a while. Mr. Grindenko is a scholar and musical seeker; he is also the choir’s conductor. He has assembled 12 men, and they work regularly in a Moscow church. At Alice Tully, they looked slightly forbidding in their black robes, a delegation from another world.

The first part of their concert offered early church music, much of it from the 16th century. One had the feeling of reaching way back, returning to roots. There is obviously a simplicity to this music, and a sameness. D minor was the key of choice – at least it was for the Russian Patriarchate Choir on Thursday night. I think they could have programmed a little less of this music, but there was no denying the authority with which they sang it.

They showed themselves a manly group, a little rough, Russian to the core. Entrances were often poor, and pitch was a problem – but their sincerity, and that authority, counted for a lot. One Easter piece began with a kind of trumpet call from a tenor: “Christ is risen from the dead.” When the rest of the group joined in, they were vigorous and convinced.

The first half of the program ended with a “Te Deum laudamus” by that fine composer Dmitri Bortniansky, who lived from 1751 to 1825. After so much primitiveness and austerity – and these are not to be interpreted as pejorative – it was as though the sun had come out.

After intermission, the choir gave us music from such composers as Rachmaninoff and Gretchaninoff. Rachmaninoff’s “Sacred Concerto: Kontakion for the Dormition of the Mother of God” is not to be confused with the Piano Concerto No. 2 – but it is still Rachmaninoff, and the music of his church was extremely important to him. Pavel Chesnokov’s “The Angel Cried Out,” from this choir, was startlingly lush and Romantic. And Gretchaninoff’s “Great Litany” marched movingly.

The program ended with a group of folk songs, the first of which was “Evening Bells.” Was I the only one in the audience who thought it started out like “Silent Night”? And who discerned in the accompaniment “The Little Drummer Boy”? Maybe. Closing the folk group was a Cossack song, “Snow, It’s Time for You to Melt!” This would be especially appropriate in late winter. The choir gave it all they had, singing stoutly and dare I say lustily.

The audience responded as for a rock group, and the choir obliged with two encores. No question about it: The Russian choral tradition has arrived.

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To conclude the Mostly Mozart Festival, music director Louis Langree led a concert boasting two of Mozart’s greatest works: the Piano Concerto No. 20 in D minor, K. 466, and that mass (in C minor). Let it not be said that the festival went out cheaply.

Soloist in the concerto Jonathan Biss, a young American. The piece started superbly, thanks to Mr. Langree’s control of it. These opening pages were dramatic, even alarming – just as Mozart intends. Mr. Langree imparted the full sweep, without being heavy-handed. And the Mostly Mozart Festival Orchestra was technically immaculate.

When Mr. Biss entered, things took a worrisome turn. His initial measures were dry and tepid. And when he got to faster passages, he rushed, ruining the excellent tempo that Mr. Langree had established. The orchestra struggled to keep up. So the first movement was spoiled fairly early on.

The pianist did some graceful playing, but mostly he lacked sparkle, color, insight. He could not stop rushing the faster passages. And what might have been taken for a Mozartean modesty was, in fact, dullness. Mr. Biss did play Beethoven’s cadenza well – with character and understanding – and what a cadenza it is.

In the slow movement (the Romance), that first sustained F did not sing at all, falling flat on the stage. But the second was better. And, altogether, Mr. Biss played this movement with more refinement and musicality than he had the first.

The opening of the last movement (the Rondo) was poorly articulated, sort of souped over. But Mr. Biss was crisper later on. And Mr. Langree had the orchestra play with wonderful fire – a thoroughly Mozartean fire. In this movement, Mr. Biss offered his own cadenza, which was a nice effort (a little Lisztian). But terribly disappointing was the D-major section with which Mozart concludes the piece. Its dawning ought to be radiant, magical. Brahms borrowed this for his own D-minor concerto. On Saturday night, however, it was unremarkable, a failure of both orchestra and pianist.

And now to that grand finale – the C-minor Mass. The four soloists were led by Sandrine Piau,a French soprano. She began uncertainly, but soon found her footing. Her high Cs were impressive, and so was a low A flat (which Mr. Langree took care not to cover). “Et incarnatusest” had due purity.

The mezzo-soprano, Tove Dahlberg, a Swede, could not have enjoyed her best night. She was a little weak and breathy, and she was also guilty of some chirping. The tenor, Gregory Turay, was solid and pleasing, and so was the bass, Patrick Carfizzi. The bass has little to do in the Mass – Mr. Langree used Franz Beyer’s version, incidentally – but he cannot be dispensed with.

As for the combined forces of the Russian Patriarchate Choir and the Concert Chorale of New York: They were magnificent, deeply to be appreciated.

In my view, there was one overall weakness in Mr. Langree’s C-minor Mass: It was peppy, springy, correct. It could have done with more profundity and grandness. Many today laugh at the Mozart of earlier conductors such as Klemperer, Krips, and Solti – let them. The laughers are all letter and no spirit, and they cannot be trusted on the letter, either.

In Saturday night’s “Laudamus te” – a mezzo aria – where was the warmth and praise? This might have been a secular ditty, a Rossini aria. When Ms. Piau and Ms. Dahlberg sang together, I sometimes thought of the duet from “Lakme.” The Mozart Mass ought to be different. Mr. Langree pepped his way through the “Domine.” And the beginning of the “Credo” might have been from “The Abduction of the Seraglio” – this is the wrong feeling. The Mass should not be heavy or overwrought, heaven knows. But it needs its dignity, its uplift, its greatness.

There were splendid moments, however: The “Qui tollis” had heart and blood, and the “Jesu Christe” had its Cmajor power. In the following fugue, you could really hear those Russian basses, and Mr. Langree conducted as though he felt privileged to do so – which he was.

His leadership of the Mostly Mozart Festival has been a boon to New York. We are only 11 months away from next season.