Classical composers usually improve as they age. Beethoven reached dizzying heights during his late period; his last few symphonies and string quartets, intensely personal meditations on human nature and God, radically altered the way composers thought about form and harmony. Stravinsky, whose upward trajectory is harder to trace, given his restless desire to explore different musical territories, produced some of his most intricately beautiful works during old age. Late periods are usually marked by mastery and introspection.

I wonder, then, what happened to Leonard Bernstein, whose late-period attempt at a masterpiece, “Mass,” is an extroverted affair of the most flamboyant kind, exhibiting a jumble of genres and conflicting musical values. The 1971 work was revived last week at Carnegie Hall as part of the ongoing Bernstein Festival, with the Baltimore Symphony Orchestra under the deft baton of Marin Alsop, herself a Bernstein protégé. “Mass” is a so-called “theater piece” with a formidable cast of three choruses (a formal choir, a children’s choir, and a group of about fifteen adults called “Street Singers”), an orchestra, a marching band, and a rock band. In last week’s performance the exuberant and talented Jubilant Sykes sang the lead role of the Celebrant, the lead priest. “Mass” is in many ways a tribute to the turbulent sixties. A crisis of faith sweeps through the congregation of Street Singers as they struggle to find meaning in the Catholic mass, a tradition now seemingly broken in a world rattled by war and assassination. (The piece was, in fact, commissioned by Jacqueline Kennedy in memory of her husband, the assassinated president.) Rock music and classical music collide. Folk music and atonal serialism butt heads. “Mass” seeks to evoke, through the visceral power of music, the anxiety with which modern churchgoers approached culture and Catholicism in the sixties.

The musical idea lurking behind “Mass” is an interesting one: a modernized interpretation of sacred mass texts, including the “Kyrie eleison,” the “Agnus Dei,” and the “Gloria in excelsis deo,” with interspersed English texts written by Stephen Schwarz (of “Godspell” fame). Biblical Latin has appeared in musical masterworks since before the Renaissance, and composers from all eras—Palestrina, Bach, Mozart, Stravinsky—have drawn inspiration from them. Even as fifteenth-century plainchants evolved into ornate eighteenth-century requiems, the religious words retained their integrity. In “Mass,” Bernstein seems to hold little reverence for the lauded texts, or the traditions that have made them so sacred in music.

Take the “Kyrie eleison,” the first large number in the work. From the outset Bernstein abandons the usual approach to setting the text—a long, brooding build-up, often fugal—and calls in the band for a rousing march. Flitting moments of counterpoint can be heard amidst the squalling brass and ever-modulating singers, but the overall impression is that of gaudy musical theater. (The children’s chorus playing kazoos certainly doesn’t help.) The “Kyrie” contains beautiful moments, including an upward-spiraling, sparsely orchestrated call-and-response between a boy soprano and the children’s choir, but the strident march motif always prevails.

Likewise, Bernstein apparently read “Dona nobis pacem,” meaning “Give us peace,” as apt lyrics for a jazzy, 6/8-meter ballad. The song, which arrives at the end of the “Agnus Dei” and combines English lyrics with the Latin, is an ironic twist on fifties tearjerkers—think “Grease.” As the number heats up into a violent struggle (cue the organ), the frustrated congregation of singers descends upon the Celebrant, forcefully bearing the message, “Give us peace, NOW!” (Cue the sax, and the wild trumpets.) In last week’s performance the visual spectacle of bodies writhing on the floor in agnostic anguish overwhelmed the elegance of the Latin text’s message. The contemplative words were distorted and then displayed in an ugly manner. Had Bernstein veered away from the song’s jazzy tone—opting instead for something less sarcastic, more gravely abrasive and dissonant—perhaps I could have taken the struggle more seriously.

Orchestral “meditations” link the show-stopping numbers; they are musical highlights. The first is a slow, dark and contemplative piece. Upon first listening I was startled by its similarity to the slow movement of Shostakovich’s Fifth Symphony—a gradual ascent in the strings leads to a climax with deathly tolls from the xylophone—but the music remains compelling in context, offering instrumental respite from the usual cacophony of singing and electric guitar. Bernstein had no quibbles about borrowing music from his contemporaries, including Shostakovich and, in other sections of “Mass,” Copland. His incorporation of their material is a tribute to their prowess. “Mass” is a veritable melting pot of contemporary music.

Show tunes fill out the production. Unencumbered by Latin, these songs recall Bernstein’s heyday as the creator of “West Side Story.” The most memorable melody in “Mass,” “God Said,” almost directly echoes the structure and mood of Anita’s Puerto-Rican hit, “America,” from the older piece. But what made “America” successful—its self-righteous ethnic pride, its snappy humor—is absent in this number, which expresses doubt over certain aspects of Catholicism. The lyrics are hopelessly cheesy (“God said, Let there be Light…/ And it was goddam good!”), the humor dated (“Let there be sprats to gobble the gnats”). Even its musical motifs, such as the singers’ whole-tone scale ascent into a grating tritone (“And it was good!”), become stale with repetition. The banjo accompaniment is successfully cute.

The Street Singers ultimately fail to forge a connection with the listener. We care little for the fortunes of these nameless characters; they are merely churchgoers who experience a “crisis of faith,” the Celebrant a struggling priest traumatized by their doubts. Effective character development requires more than such simple motives and relationships. Schwarz and Bernstein attempted to fill out some of their stories with monologues, but the sensual overload and whirling speed of the production overrides plot development at every turn.

Considering “Mass” as the apex of Bernstein’s composing career is difficult. In context, its raw appeal becomes clearer. Bernstein was a celebrity. He led a public life as conductor of the New York Philharmonic, and strived to bring classical music back into American consciousness. The sixties heralded a culture of confusion, as like-minded youths struggled over distinctions between art and commerce, the high and the low. How else could a charismatic figure like Bernstein culminate his career in the early seventies, but with rattling brass and contemplative strings, with fire and agnosticism? Bernstein’s take on the mass is a tribute to a new America where Catholicism and other faiths must embrace all types of people and where rock and roll heavyweights are the new religious icons. The music has its shortcomings; Bernstein’s vision has none.