The task confronting new-music composer Lansing McCloskey in his 90-minute choral work Zealot Canticles couldn't have been more formidable: How to dramatize a combustible text by social activist Wole Soyinka about hallucinating during a hunger strike (among other things) without preaching to listeners.

The stakes get higher: The texts chosen for this piece were spread over 20 movements, most of them with sound worlds and expressive intent that was highly distinct from the others.

McCloskey and Crossing director Donald Nally have said they were keen to differentiate between persons who are passionate and those who use their convictions dictatorially. The key phrase sung in the piece: "I am right, you are wrong, I am right, you are dead."

The Soyinka texts were compiled from writings both by and about the Nigerian activist, who was jailed for two years, often in solitary, and who underwent a near-death hunger strike. During desperate times, he employed the mantra "I need nothing, I feel nothing, I desire nothing" that was used in Zealot Canticles in an appropriately reoccurring manner.

The Canticles premiere Sunday by the Crossing choir at the Presbyterian Church of Chestnut Hill was a rhetorical success. Audiences were galvanized. Musically, though, few composers are likely to write 90 minutes of consistently good music on the first attempt, even when the task is self-assigned, especially in a piece of such length and emotional complexity. The opening movements had McCloskey mapping out the playing field in ways that were a bit earthbound and tedious. Once established, that playing field was explored with all possible options, not all of them optimum.

Choral writing was often divided between men and women. Soloists emerged from the mix, but never in the same way twice.  Solo clarinet was almost ubiquitous in the small instrumental ensemble and was always an eloquent emotional point of reference, especially as heroically played by Doris Hall-Gulati.

Less interesting was the string quartet writing, which often played softish, vaguely dissonant accompaniment that suggested a Renaissance viol consort with a low-grade headache. Narrative passages somewhat resembled Ralph Vaughan Williams' way of airily diluting major and minor keys, thus avoiding conventional emotional polarities, though there were times when you wanted to tell the composer, "Say what you mean."

That was mostly in the first half. The second half had extremely compelling music, often in the manner of late-period Benjamin Britten, who used uningratiatingly spare means to achieve precise dramatic effects, momentum be damned. Sometimes McCloskey stayed away from inflecting the text, preferring big-picture techniques, such as juxtaposing two simultaneous musical gestures in separate, alien keys.

The "I am right, you are wrong" passage was set in the unlikely manner of a lullaby, an act of friendly persuasion with the gentle repetition of "I am right." The "Dog in Dogma" movement had a high-range soprano solo in a fragmented high-velocity rant about Marxism, Buddhism, etc. while the chorus shouted out words like splat! and pig.

A baritone solo declaring that polite parlance isn't blunt enough in times of crisis unfolded over a stable, even breezy orchestral ostinato until it quoted Langston Hughes: "There is no lavender word for lynch," bringing the movement to an appropriately screeching halt.

A sardonic meditation on superstition and Satanism had a gradual harmonic evolution that built, almost as your aural back was turned, with slow-creeping horror. The single best movement conveyed a sense of Soyinka's hunger strike: Everything felt eerily distant -- whether words or instruments -- ending with the "I need nothing" mantra.

With so much good stuff here, McCloskey might owe it to his piece to make another compositional pass through it. Or two. The world needs this piece -- and needs it to be as good as it can be.