Salvator Mundi, the portrait of Christ by Renaissance master Antonello da Messina, stares through you.

It doesn't matter how you address the beneficent visage, which looms over the stage during On the Concept of the Face Regarding the Son of God. It doesn't matter whether you believe in Jesus as a divine power; his gaze burrows into you as it burned into Romeo Castellucci.

"He called me as a man, not as God," says the provocative Italian theater practitioner, whose play runs Thursday through Saturday at the Suzanne Roberts Theatre as part of the 2013 Fringe Festival.

By the end of the play, conceived and directed by Castellucci, the portrait will be as battered and smeared with excrement as the play's principal character, an incontinent old man who is cared for by his dutiful son.

The combination of excrement, the Jesus backdrop, and the elderly actor inevitably stirs controversy, not only because Castellucci raises the question of God's absence in the face of suffering (or his presence - the director traffics in abstracts without answers) but because of the manner in which he deals with decay and death.

"It's a story about love, tenderness," says Castellucci during a Skype interview from the offices of Socìetas Raffaello Sanzio in Cesena, Italy. "This belongs to Christian tradition, but it is not direct."

For Castellucci, the portrait and the play's portrayal of end-of-life issues represent beauty and conflict as told through metaphor - what it means to believe in God and not to believe, in one breath. "I chose this portrait, then imagined terrible conditions as an answer to terrible beauty."

Such provocative duality thrilled FringeArts impresario Nick Stuccio when he saw Castellucci's Concept in Montreal last year. In Castellucci, he found a transgressive artist whose visceral theatricality refuses to go down easily.

"He moves slowly through real time, offering up big philosophical questions without being obvious," says Stuccio, who sees Concept not as a treatise on religion but rather as a taboo-breaking story about systems, the conceptual notion of Christ. "God's not here, he's an abstract idea. In that absence, we're left to grapple with what Christ is."

Castellucci has grappled with the idea of faith, but ask him if he believes in God, Jesus, or Catholicism, and he says the answer is of no consequence to his aesthetic.

"That is a personal question, unimportant to the story," he says. "Religion is not my métier. In any case, I am full of doubt."

Doubt, but not disavowal; the contradiction of which Castellucci speaks - one that rears its head toward the play's finale, when the phrase "I am Your Shepherd" appears, followed by "NOT" - stems from Psalms 22 and 23, which read, respectively, "My God, my God, why hast thou forsaken me?" and "The Lord is my shepherd; I shall not want."

Says Castellucci, "Right next to each other, we get the full representation of our conflict with God."

Castellucci sees himself as a conduit, posing questions that only theater and religion can. "They are sisters, theater and religion, born in the same time. It is natural, a choice to tell this story in that way."

The role of excrement in the play is as crucial as the relationship between the old man and his son. Rather than think of it as degrading, Castellucci recalls waste being seen as a joyful gift. "It can signal indignity, but, psychologically, in childhood, [feces] is seen as a gift from a son to the father."

The old man and the young man? Metaphors for God and Jesus?

He smiles. "I know this metaphor. It's possible, but not my goal. The Bible is full of fathers and sons. You can look at this as a competition between generations, as political struggle. The story is a prism."

Stuccio says that as Castellucci puts distance between himself and God, there is a void. "We need someone to talk us through this void, hence Bill Golderer," says Stuccio of the pastor of Philadelphia's Broad Street Ministry, which is the co-presenter of Concept. Golderer will lead a postshow discussion on opening night.

"BSM has a unique role, as home for the artistic soul trying to grasp the beauty and pain of this world," he says of his sprawling church on South Broad Street, which ministers - with intelligence rather than pity - to some of the city's less fortunate. "That ideal sits within a larger societal vision for human flourishing, where every Philadelphian - without exception - has access to everything to experience the fullness of life, from delicious food to the arts, which act as an anchor to this vision."

There is no greater anchor than a meaty play without easy answers. When Stuccio proposed Concept to Golderer, he took it on blind faith: "BSM favors art more suggestive than safe."

When it comes to Castellucci's shredding of Jesus' image, Golderer's institutional side comes out swinging - softly.

"I can understand why this piece provokes strong reactions from people who possess deep Christian faith," he says. "The face of Jesus as we experience it here appears by turns indifferent and apparently unmoved by the anguish and suffering depicted in the events of the play."

It's not a depiction that resonates with Golderer. "Later in the piece, as actors take out their frustration on the image of Jesus, it leaves those of us who have grown to love Him in an awkward spot: How should we feel about the one in whom we believe being defaced?"

Golderer says his relationship with God involves a more durable deity. "God doesn't solely want a relationship with you when you're on your best behavior. Who in the end needs a fair-weather divinity or a God not vast enough to absorb my anguish and doubt, one only interested in my impulse to praise?"

In his mind, God wants total honesty. "This play is honest," he says. "God can handle that. Our faith certainly should, too."

On the Concept of the Face Regarding the Son of God

7 p.m. Thursday through Saturday at Suzanne Roberts Theatre, 480 Broad St. Tickets: $20-$39. Post-show discussions all three nights; 5:30 p.m. pre-show talk with Romeo Castellucci on Saturday. 215-413-1318 or www.fringearts.org