"Hesperus Is Phosphorus," Lewis Spratlan's New Work In the section of David Eagleman's work of fiction "Sum: Forty Tales From the Afterlives" called "Egalitaire," a mature female God is imagined mulling the difficulties of arbitrating morality. Vespers Cantata: Hesperus Is Phosphorus, by the Pulitzer Prize winner Lewis Spratlan, in its New York premiere at Park Avenue Christian Church, with the chamber choir the Crossing, conducted by Donald Nally. "Dividing the population into two categories - good and bad - seemed like a more reasonable task when She was younger," Mr. Eagleman writes, "but with experience these decisions became more difficult." Such are the musings of critics too, as I could not help thinking when I heard those lines from "Sum" as set by the composer Lewis Spratlan in his new "Vespers Cantata: Hesperus Is Phosphorus," which had its New York premiere on Tuesday evening at the Park Avenue Christian Church. The work uses texts from an unlikely variety of sources, including Wallace Stevens and Wallace Shawn, drawn together by the theme of dissolving, of the impossibility of identity's remaining constant and unified. As with the human beings that Mr. Eagleman's God despairs of clearly judging, Mr. Spratlan's cantata is neither entirely good nor entirely bad. Lasting about 70 minutes, it is a long, slow haul whose inspired moments end up highlighting that much of the score has a discouraging sameness. But those clever passages should not be discounted: they shine as examples of what this lovingly made work could have been. And on Tuesday "Hesperus Is Phosphorus" also had the benefit of a polished performance from two ensembles from Philadelphia: the Crossing, a chamber choir, and an acute instrumental sextet drawn from the ranks of the Network for New Music Ensemble. Mr. Spratlan is best known for his opera "Life Is a Dream," which won the 2000 Pulitzer Prize for a concert version of its second act, a highlight of its long gestation. Begun in 1975, the work did not receive its first full performance until 2010, at the Santa Fe Opera. Like a true opera composer Mr. Spratlan writes sensuously for voices, and the choir sang with resonant depth, easygoing in another lengthy excerpt from "Sum" and carefully building in intensity through a setting of the "Esurientes" from the Magnificat. The best things in the work are the strangest, like the bluesy, lilting clarinet line at the start of the setting of Adrienne Rich's "Stepping Backward" and the wittily Gregorian chant-style austerity of the line "He's on a romantic junket with his girlfriend" in a litany of possible places God has vanished to. Too much of "Hesperus Is Phosphorus" lacks this charm, and too often the score settles into a rote voice: lyrical in feel, gently dissonant in flavor, meandering even in its peppy sections. Mr. Spratlan's treatment of the final "Amen" could stand for the work as a whole. It is not without prettiness and skill, but, circling through iteration after iteration, it lingers rather too long.