Mileage may vary on the way “Attachment” uses an already too frequently maligned religion as a foundation for supernatural scares, but that’s also kind of the point of writer-director Gabriel Bier Gislason’s feature debut: With this possession story set in an Orthodox Jewish household, the Danish helmer disorients what may be a good portion of his audience by thrusting them into an unfamiliar belief system and asks if it’s them or those performing its rituals who are strange or misguided. Led by Josephine Park as a woman navigating a new relationship in the shadow of her lover’s seemingly disapproving mother, the film mines romantic, familial and religious discord while swapping out the usual Christian boogeymen for less common Jewish ones.

Park plays Maja, a former actor now staging readings to children in character as the Christmas elf she played on television. After a meet-cute collision in a library with Leah (Ellie Kendrick) where the two of them mix up their books, Maja invites the Jewish academic home for tea, and before long they’re canoodling in her flat. But when Leah has a seizure that results in a serious injury, she returns to London to be properly cared for by her mother Chana (Sofie Gråbøl). Maja, free from responsibilities and eager to explore new love, volunteers to tag along.

Though Leah indicates that she hasn’t held onto many of the traditions of her Orthodox upbringing, Chana is fiercely devout and oppressively controlling of her daughter’s behavior — and being largely bedridden only encourages her mother to be more involved in her life. The seemingly naturally anxious Maja fumbles through her initial interactions with Chana, and ventures into their family’s predominantly Jewish neighborhood to seek a book that might orient her with the practices of their faith, which seem exclusionary to her and invasive to Leah.

Armed by local bookseller Lev (David Dencik) with a dangerously small bit of knowledge about their customs, Maja makes further overtures to be nice. But when Chana finally lets her guard down just enough to open up about herself, she offers not the admonition Maja expects for their same-sex relationship but an ominous and unspecified explanation that she is trying to protect her daughter from something that this newcomer — and outsider to the Jewish faith — cannot understand.

Uncertain whether it’s her ailing partner or that partner’s rigid, obstinate mother who is not being entirely honest, Maja is forced to choose whether to stand by Leah’s side or acquiesce to Chana’s parental control — behavior which despite her insistence is for her daughter’s own good, does not seem to be improving Leah’s physical or mental health.

Two or more decades ago, a story like this would unfold only on one level, following a young lover (who would likely be straight) encountering the encroaching menace of their partner’s parent or loved one. That alone, amplified by a natural division like the one between Leah’s Jewish background and Maja’s as a Christian or atheist (her religious convictions are never explored) would be more than enough to elicit suspense — and would culminate in some kind of a violent, reductive showdown that would do no favors to people of any faith. By comparison, “Attachment” skillfully employs Leah and Chana’s belief system as a barrier that Maja, an outsider, cannot penetrate. Not only does the film avoid vilifying these devout characters and their behaviors, but it uses them to create the central threat to the relationship between Maja and Leah — and also its ultimate solution.

As a storyteller, Gislason tends toward an angularity to the suspense that goes right for moments of unease or tension, be they social or (possibly) supernatural; the consequence of this is that Leah spends too much of the film principally defined either by various states of sleeping/dreaming, or rushing out of conversations that it’s clear Maja (and by extension the viewer) would like to resolve with even a little more clarity. But he also moves familiar beats to moments earlier in the story than expected to showcase that his aim is not to exploit the language of Judaism and its spiritual phenomena (“golems,” “dybbuks” and so forth) to scare audiences but to depict with thought and sensitivity how these beliefs shape the behaviors of individuals in that community, and in perhaps heightened circumstances they can help or heal them.

That it also manages to be an unsettling tale about a slightly lost woman whose new love leads her into a family afflicted by demonic possession is a testament to the virtuosity with which the first-time feature filmmaker wields both the rites of his own religion (he’s Jewish) and the conventions of would-be scary storytelling. For horror fans that are as compelled by creative (and thought-through) ideas as by style or skillful execution, “Attachment” embraces what to many may be a new or different text, but it’s clearly knowledgeable about the traditions of the genre — and most of all, deeply faithful to its spirit. Amid a rash of brutal horror movies, Gislason’s debut is safe and nonviolent enough to take a squeamish partner to on a first date; but unlike the short-term gagging more violent entries induce, the fears and uncertainties it explores about relationships, romantic, familial and religious, seem a lot likelier to prevent a second one.