The center of gravity of “The Whale” is obviously the 600-pound man at its center. Look closely, though, and he’s the one with a soul as light as a feather.

Charlie is a reclusive, morbidly obese English literature teacher unable and unwilling to stop eating himself to death. As his health woes mount and his life expectancy is put at just a week, Charlie struggles to reacquaint himself with his estranged daughter. We meet him on Monday and the film goes day by day to Friday.

Charlie is a gentle giant, not raging at his fast-approaching demise. He’s an optimist and a fierce believer in truth even though there is nothing in his world reinforcing either. “The Whale” is not always pleasant to watch but the payoff and performances make it an astounding film.

Stationary and wheezing on his couch, Charlie is repeatedly visited by a constellation of people — a friendly nurse, his teenage daughter and a young missionary from an apocalyptical church. They all need something from this well-meaning but broken man — spiritual, medical or familial. They are all broken, too.

The movie, based and adapted from the off-Broadway play of the same name by Samuel D. Hunter, is directed by Darren Aronofsky, who helmed such dark tales as “Requiem for a Dream” and “Black Swan.” Hunter’s depiction of the mortification of the flesh perfectly meets a director enamored by the grotesque.

Brendan Fraser has earned lots of Oscar buzz for playing Charlie, allowing his signature puppy dog face to remain despite a massive body suit and swelling prosthetics. And why not? It is one of the most moving performances in years, full of humanity and a redemptive triumph for an actor who hid his talent in quickly forgotten films like “Blast from the Past,” “Hair Brained” and “Airheads.”

The whole cast is perfect, from Sadie Sink as Charlie’s spiky daughter, Hong Chau as his foul-mouthed nursing angel, Ty Simpkins as the missionary with a hidden past and Samantha Morton as his ex-wife with simmering anger and yet still love. There are steady references to Herman Melville’s “Moby Dick,” which gives the film the title and its doomed vibe.

Charlie has ballooned ever since the death of his same-sex partner, who apparently willed himself to death by wasting away in starvation after their relationship was condemned by his church-leading father. Charlie has apparently decided to die the opposite way.

He is sadly apologetic to his nurse — “I’m sorry,” he says continually — and shuts the video camera on his laptop during his online classes. Even the pizza delivery man doesn’t know what he looks like. “Who would want me to be part of their life?” he asks.

There has been fear that the film might be fatphobic and it’s true that cinematographer Matthew Libatique often leans into unflattering ways to show Charlie, soaping in a shower, straining to stand up or touch the floor, covered in sweat and shoving pizza or fried chicken into his mouth. Maybe some of that could have been touched on instead of lingered on.

But body weight is not what the writer and director want to focus on here. It’s more the weight of guilt and love and faith. “I just want to know I did one good thing in my life!” Charlie shouts. One feels that the underlying issue in “The Whale” could have been obesity as easily as cancer or alcoholism or a blood disorder. Hunter is exploring salvation, redemption, determinism and family.

The play has been sharpened for the screen but there’s no escaping the fact that it is rooted inside Charlie’s Idaho apartment, which he shuffles about in on a walker or later a wheelchair. This doesn’t make for sweeping cinema. Sometimes the apartment feels confining like a ship, adding to the Melville theme.

Some of the filmic attempts are forced, like the symbolically heavy bird that Charlie feeds outside his window, the three times actors rush to leave the apartment only to stop and turn back, and the heavy rain that builds as the film’s climax nears. But this is a film that stays with you and changes you. It is heavy, indeed.

“The Whale,” an A24 release that is in movie theaters on Friday, is rated R for “language, some drug use and sexual content.” Running time: 117 minutes. Four stars out of four.