“Calvary” opens Friday at Sundance Cinemas. R, 1:40, three stars out of four.

John Michael McDonagh’s “Calvary” has a corker of an opening scene. Father James (Brendan Gleeson), a kindly village priest in County Sligo, is in the confession box, and an unseen parishioner walks in. He tells how he was sexual abused by another  priest as a boy. The man then vows to kill the good priest in one week as revenge against the church.

“It’s certainly a startling opening line,” Father James responds drily.

But if you are expecting “Calvary” to be a wicked crime comedy in the vein of McDonagh’s previous collaboration with Gleeson, “The Guard,” think again. “Calvary” is many shades darker, a nearly pitiless examination of the human condition and the seeming futility of faith. There are some laughs, especially in the first half of the film, but they tend to stick in your throat as the film goes deeper and darker.

Gleeson attempts to figure out who the murderous member of his flock is, and learns that everyone is a possible suspect, from the wealthy sociopath who lives up on the hill to the adulterous doctor (Aiden Gillen), from the cuckolded butcher (Chris O’Dowd) to the mass murderer at the local prison (Domhall Gleeson, Brendan’s son).

But if you’re watching “Calvary” as a whodunit, you’re doing it wrong. It could be any of them, which is really the point. This is a community whose faith has been rattled by everything from personal tragedy to the clergy abuse scandals. Everyone in town seems to be either questioning their faith, or openly mocking the priest for clinging to his. The other priest in Father James’ parish doesn’t seem to care, seeing himself more as a middle manager than a spiritual leader.

Rather than try to save his life, Father James finds himself trying to save his faith in the wake of such scorn. Gleeson is magnificent here, falling farther and farther into despair as one parishioner after another turns their back on him. He’s such a bear of a man, but all that physical prowess is largely useless for a priest trying to save hearts and minds. Instead, he’s the victim of mockery at the local pub, vandalism and worse at home. If you know what Calvary refers to in the Bible, you know the parallel McDonagh is going for here.

“Calvary” is at times brutal to watch, not so much for its onscreen violence (although there is some) but its view of humanity as essentially selfish creatures looking for a higher power to blame for their misery, and one good man among them who seems powerless to change their minds. There are a few redeemable characters, especially Kelly Reilly as Father James’ estranged daughter and the great M. Emmet Walsh as a reclusive writer fond of his talks with the good Father.

The film ends with the faintest glimmer of hope, but even that hope comes wrapped in despair, suggesting that we’re each all we have to rely on. Because the man upstairs isn’t answering our calls.

“Calvary” is a very ambitious film for McDonagh, and there are times it seems he’s bitten off more than he can chew, as the movie lurches wildly from one tone to another, McDonagh falling back on genre conventions occasionally. But it stays with you, for sure.