Does God have a plan for each of us? If so, how can we discern it and live accordingly?

John Irving's 1989 novel, A Prayer for Owen Meany, explores these questions in depth, mixing black comedy with heart-rending tragedy in a universe peopled with outsiders and grotesques. Simon Birch is the oversimplified, cleaned-up movie version of that best seller. The changes from the original are far-reaching enough that Irving requested that the credits show the film as only “suggested by” his book, rather than the more usual “based on.”

What's left is a sweetly sentimental tale about a 3-foot, deformed adolescent named Simon Birch, who believes that he must live out God's plan for him. First-time director and screenwriter Mark Steven Johnson, who penned the Grumpy Old Men series of feature-film comedies, preserves some of the book's theological musings about the power of forgiveness and the hypocrisy of organized religion. But his main intent is to play on our heartstrings.

The movie's first image is of a stained-glass window of Jesus and his disciples in the Episcopal church of a small Maine town. A grown-up Joe Wenteworth (Jim Carrey) is visiting the grave of his childhood friend, Simon Birch, whom he describes as “the reason I believe in God.”

The action then flashes back to the mid-1960s as Joe explains why he is a believer.

Simon's parents are stereotypical, flinty New Englanders who are embarrassed about their son's dwarfish size and his cracked voice which sounds like “strangled mice.” The young boy himself is aware of his condition's effect on other people and protects himself with a salty wit. He also has an ordinary adolescent's libidinal urges.

Determined to lead as normal a life as possible, the 12-year-old attaches himself to the more prosperous, if dys-functional, Wenteworth family. Joe Wenteworth (Joseph Mazzello), who's the same age, is his best friend, and Joe's unwed mother, Rebecca (Ashley Judd), tries to make up for the love Simon never gets at home.

Simon proclaims his religious faith to anyone who'll listen. Joe is an atheist, and the two on occasion heatedly debate the meaning of life. But Simon's main theological adversaries are associated with the local Episcopal church. He often argues with the rector, Rev. Russell (David Strathairn), during Mass. When the priest announces there will be coffee and doughnuts after the service, Simon declares to the astonished congregation: “Who said God is interested in a continental breakfast?”

The filmmaker is determined to make the point that organized religion is often the enemy of true holiness, that its faith can be secondhand and lukewarm. Rev. Russell depresses the 12-year-old by telling him he doesn't believe God has a plan for everyone, and Simon's Sunday School teacher (Jan Hooks) thinks his fervor upsets the other students and continually picks on him.

Despite his condition, Simon is a pinch-hitter on the local Little League team. While his size makes it difficult for pitchers to do anything but walk him, the one time he does hit the ball, it accidentally strikes Joe's mother and kills her. Simon is devastated by the loss of the only adult in the world who seems to love him. In one of the movie's most moving sequences, Simon receives Joe's forgiveness for his mother's death. To show his gratitude, Simon promises to help Joe discover the identity of his real father, an issue which has tormented him for most of his childhood.

While straining to make symbolic points, the filmmaker continues to poke fun at organized religion. The Sunday School teacher organizes a Christmas pageant with Simon as the Baby Jesus because he's “the only one who fits into the manger.” The event disintegrates into chaos when Simon makes a play for the actress portraying the Virgin Mary. For this blasphemy, Rev. Russell rightly punishes him — though it is clear that the filmmakers intend the viewer to see Simon as some kind of Christ figure and as always in trouble with church authorities.

However this idea may have worked in Irving's novel, it seems labored up on the big screen. Yet Simon remains steadfast in his belief that he is “God's instrument,” and eventually he gets a chance to put himself to the test.

Simon Birch will certainly make you laugh, and it may even make you cry. Your heart can't help go out to the feisty, undersized boy whose upbeat spirit and sense of humor help him cope with adversity. His religious faith is always treated with respect. But the filmmaker is unable to strike the proper balance between his story's emotional core and its spiritual themes. The result is an uneven hybrid — part tear-jerker, part theological speculation — a comedy-drama unsure of its own identity.

Arts and Culture correspondent John Prizer writes from Washington, D.C.

Simon Birch is rated PG by the Motion Picture Association of America.