John Michael McDonagh’s 2011 debut, "The Guard," provided the wonderful Brendan Gleeson with a vehicle for some of his best screen work, playing an Irish West Country cop unencumbered by diplomacy skills. But "Calvary," the follow-up collaboration of the writer-director and lead actor is in a whole different league.

Gleeson’s performance as a man of profound integrity suffering for the sins of others is the linchpin of this immensely powerful drama, enriched by spiky black comedy but also by its resonant contemplation of faith and forgiveness. Representing a considerable leap in thematic scope and craft for McDonagh, "Calvary" deserves to reach the widest possible audience.

As with the work of McDonagh’s younger brother, the playwright, screenwriter and director Martin McDonagh, an inherent irreverence is essential to both "The Guard" and this film. But don’t let the gags, the ripe profanity and the wicked comic characterizations fool you. The director of "Calvary" appears utterly serious about exploring the uses and abuses of spirituality in a world of toxic disillusionment and cynicism.

Set along the rocky cliffs of County Sligo, the film begins in the intimacy of a Catholic Church confessional box. Father James (Gleeson) listens as the voice on the opposite side of the covered window recounts being sexually abused by a clergyman from the age of 7. The unseen parishioner informs the priest that he’s giving him a week to make his peace with God and the world, arranging a Sunday meeting on the beach where he intends to kill him. Since the man who molested him died long ago, he reasons that the death of an innocent priest will make more of a statement.

This would seem an irreversibly grim departure point for a film. But McDonagh and the actors navigate supple shifts between mordant humor and emotionally complex drama throughout much of "Calvary."

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Father James appears to have recognized the voice, and while he seeks counsel from the bishop (David McSavage), he declines to name his prospective murderer, even later when a violent warning suggests the seriousness of the threat. Instead, in what amounts to an anticipatory whodunit that’s equal parts Agatha Christie and Stations of the Cross, he makes his regular parish rounds.

He meets with the cuckolded local butcher (Chris O’Dowd), his tarty wife, (Orla O’Rourke) and her occasional lover (Isaach de Bankole). Further encounters follow with a semi-reclusive American writer (M. Emmet Walsh), a smug financier (Dylan Moran) and an atheistic, coke-snorting doctor (Aiden Gillen). There’s also the police inspector (Gary Lydon) and the cop’s regular rent boy (Owen Sharpe).

McDonagh’s crackling dialogue makes the priest’s exchanges with the townsfolk so frequently hilarious that you don’t really notice the sobering shift that has taken place. Each of the parishioners goes out of his or her way to challenge Father James’ convictions.

Absorbing the constant criticism with forbearance and only rarely rising to the bait, James is a firmly centered man, and Gleeson etches a lifetime’s worth of knowledge, experience and hard-won serenity into the ruddy face behind his snowy beard, even if he’s not without acknowledged flaws.

Inevitably, the pressure of his looming Sunday date and the barbs of his parishioners get under his skin, and when Father James folds, Gleeson’s crushing admission of emotional defeat is shattering. There are several haunting scenes that expose the depths of the man, but none more so than when he talks candidly and without religious platitudes about faith with a freshly widowed French tourist (Marie-Josee Croze).

This is a film of rich layers — glorious comedic highs are interwoven with meditative moments and flashes of startling hostility and violence. Visually, intellectually and emotionally, McDonagh’s film is one to savor.