You get a strong whiff of salvation watching actor/playwright Rinde Eckert as Reinhart Poole, a character based on legendary Protestant theologian, Reinhold Niebuhr, in Eckert’s music-theater work Horizon. I think it was even true for the people sitting on either side of me who napped during much of the intellectually rigorous, yet emotionally satisfying, 90-minute piece.

Niebuhr’s stature derived from his postwar advocacy of Christian Realism—the idea that a kingdom of heaven would be impossible to achieve on earth because man is innately corrupt. Using a collage of spoken dialogue, arias and recitatives, Eckert, who was a finalist for the 2007 Pulitzer Prize for drama, has retrofitted Niebuhr’s postulations to ponder our own era of fundamentalism and the extremist violence perpetrated in its name.

Poole’s fictional fate contrasts with that of Niebuhr, who died in 1971. For example, Niebuhr’s writings were so seminal that he was one of the very few postwar philosophers to be as intellectually attractive to the left as to the right—someone Martin Luther King Jr. could read and admire, someone anti-Communist reactionaries could claim as their own.

Played by Eckert as an emotionally distant, melancholy, sallow figure, Poole at the top of the play has been pressured by church powers to resign his position as a Christian ethics teacher; as you walk into Horizon, you see Poole upstage, composing his final lecture. It’s clear that a torrent of emotion is pouring out of him; you notice it in Eckert’s darting eyes and again when you hear his sweetly haunting operatic tenor. When not preparing lecture notes (which is often), Poole amiably chats with his wife, debates spiritualism with his dead brother’s ghost and pursues his favorite hobby: writing an allegory about two brick masons building and demolishing the foundation of the same church for more than 1,700 years.

All the roles beside Poole’s are played by David Barlow and Howard Swain, dressed like street urchins fresh off a Housing Works shopping spree. They play women and men, as the fractured narrative requires, and toss cinderblocks around as if they’re weightless: a stunning metaphor for the fleeting and fungible nature of belief, and one that only hits you once you’ve left the theater. As a counterweight to Eckert’s blue Poole, they’re both comic relief and an emblem of Eckert’s moody meditation on the true nature of the dedicated deist.

The sleeping patrons beside me awakened midway through: It would be unnatural to remain unstirred by some of the arias Eckert offers. Prior to one aria, the bricklayers have arranged all the cinderblocks into a wide symmetrical wall—another foundation. Poole then dismantles the wall bit by bit, block by block, as he mourns our society’s hijacking of religion by political opportunists:

When I think of all the beauty in the Bible
And how abused it is by smug misguided fools
Who make of it a weapon; who make of it a golden calf
I despair that we may never have the tools
We may never have the patience it requires
In our eagerness to judge
We threw all reason on the fires.

I do not think a finer warning—or prayer—for humanity has ever been heard.

Through July 1. New York Theatre Workshop, 79 E. 4th St. (betw. Bowery & 2nd Ave.), 212-239-6200; $50 (Sun. performances $20).