This film was made at a time when priests were venerated. Just that same year Bing Crosby won an Oscar for Going My Way. The oddness of good-looking men becoming celibate didn't seem to strike people back then, I guess. If a movie is made about a priest these days, he's seriously messed up, or if he's a good guy, he has a way with a gun or kills vampires.
But back in '44, a priest was a spiritual hero, and I don't know if even Bing Crosby could have matched up against Peck's Father Francis Chisholm, who spends his career in a mission in China.
The film opens in Scotland (as in all his roles, Peck does not attempt accents) with Roddy MacDowell playing young Francis. He witnesses his parents die due to anti-Catholic violence, and is raised with friends of the family, including a girl. He grows up wanting to marry her, but attends a Catholic college, where he is finally persuaded to become a priest.
His first few curacies are failures, so he is sent to China, where he finds the church in ruins and most Chinese against him. The Chinese will go to Church if they are given money or rice, but he wants only true Christians. He is helped by a true Chinese Christian (Benson Wong) and together they open a dispensary. Peck, armed with only a medical book, saves the life of the local Mandarin, who thanks him by helping him rebuild.
The film is framed by Peck as old man. He is back in his old parish in Scotland, and a Monsignor (Cedric Hardwicke) is bent on getting him to retire. But he reads Peck's journal, and realizes all the good he has done.
Directed by John M. Stahl, produced by Joseph Manckiewicz, and written by Manckiewicz and Nunnally Johnson (you don't get much better than those two) The Keys of the Kingdom is solidly made and unabashedly sentimental. One of the subplots is when three nuns arrive, and the Reverend Mother (Rose Stradner, who happened to be Mrs. Manckiewicz) are at odds. She has the sin of pride, and can't see herself as equal to the Chinese, but she of course will come around in a very moving scene. We also get Vincent Price as a preening bishop, so not all the clergy in the film are held in high esteem.
There are some other familiar actors here, such as Edmund Gwenn as Peck's mentor, from the twinkly Barry Fitzgerald school of priests (he likes to fish) and Anne Revere as the wife of a Methodist missionary. There are also some non-Chinese actors playing Chinese roles, which isn't done so much anymore (except for Emma Stone in Aloha). But viewed in the time period in which it was made, The Keys of the Kingdom has a lot to admire, least of all the usual expert acting by Peck.