From: Gene D. Phillips, Major Film Directors of the American and British Cinema, Associated University Presses: Cranbury, NJ (1990), pages 232-234:
Joe (Jon Voight) is himself taken advantage of repeatedly by the assortment of tough and desperate individuals he encounters in the course of his descent into the netherworld of New York's slums, and at one point it looks as if he will become as ruthless as the rest. But he makes a friend of Ratso Rizzo (Dustin Hoffman), a repulsive-looking bum who needs companionship as much as Joe does; and the two take refuge in each other's friendship. Their relationship is not homosexual, Schlesinger points out; rather the story shows "how two men can have a meaningful relationship without being homosexual."
The film is faithful to the novel on which it is based, but Schlesinger and screenwriter Waldo Salt exercised more freedom in adapting it than had been the case with Far from the Madding Crowd. The first third of the novel, dealing with Joe's lonely youth, is compressed into a few fragmented flashbacks as he makes his way cross country by bus. These flashbacks indicate how unsuccessful Joe's search for friendship and love has been up to this point and hence explain why Ratso is fulfilling a real need in Joe's emotional life.
There is an interesting religious dimension that becomes apparent in the film when one examines it in depth. While Joe travels cross country on his way to New York, his Bible-belt religious formation is sketched for us as he listens to a faith healer preaching over his transistor and notices through his bus window the words "Jesus Saves" painted on the roof of an abandoned shed.
Once in New York Joe meets a Mr. O'Daniel (John McGiver), a religious fanatic who tries to force Joe to pray with him before a garish statue of Christ that flashes on and off like a neon sign. As Joe escapes from Mr. O'Daniel's shabby hotel room, Schlesinger intercuts shots of Joe's boyhood baptism in a river. The frightened boy is plunged into the waters while a hymn-singing congregation watches from the bank.
Though Joe's religious experiences have not always been pleasant, there is inbred in him a need for some kind of religious belief to give meaning and purpose to his life. Significantly, the only friend that Joe makes in New York is Ratso, an Italian Catholic from the Bronx, who sleeps in the condemned tenement they share with a picture of Christ hanging over his bed. Small church candles provide illumination at night because the electric power has long since been shut off. Joe, in turn, sings himself to sleep on occasion with one of the old hymns he learned as a boy, about receiving "a telephone call from Jesus."
After a visit to the grave of Ratso's father, Ratso discusses the afterlife with Joe, who tries to dismiss the conversation as "priest talk." Ratso counters that he is not talking "priest talk," but about what people believe in. Joe, somewhat embarrassed, admits that he thinks about such things too. At another point Joe accepts a medal of Saint Christopher, patron of travelers, from a pathetic middle-aged homosexual, who gives him the assurance that "you don't have to be a Catholic to wear it."
These and other religious references in the film have a cumulative effect on the viewer. "Is God dead?" a bishop asks rhetorically in a TV sermon we see at one point. One might be tempted to answer "yes" -- at least in the corrupt world in which Joe finds himself among the low life of New York's slums. And yet these isolated bits and pieces of religious ritual that appear throughout the film are like so many souvenirs of a faith that has somehow been mislaid, but that the owners have never completely abandoned hope of finding again. It is true that Joe does not have his faith in God strengthened in any explicit way in the picture. But, through his friendship for Ratso, he does have his faith in mankind restored, and that in itself is significant.