Flannery O'Connor's stories often deal with God and religion, and these components are present in "The Life You Save May Be Your Own;" the universal theme I find in this short story deals with elements related to religion: salvation and redemption. The story of Mrs. Crater and Mr. Tom Shiftlet concentrate on:
an individual’s ability to find opportunities for salvation and redemption in everyday life.
It would seem that Lucynell, Mrs. Crater's daughter, is the only innocent in the story—the one truth her mother shares with Shiftlet. Lucynell is deaf, though quite able to help around the house and yard—a selling point Mrs. Crater shares with Tom. She is also described as "an angel of Gawd." And an angel she may well be, in that she has not been corrupted as has her mother is.
Mrs. Crater's name denotes an "emptiness," like a crater in the earth or on the moon. She is a manipulative woman who is willing to trade her daughter to get Mr. Shiftlet to stay. When she describes Lucynell on her wedding day, though it sounds as if she is complimenting her, Mrs. Crater is alluding to the fact that the girl is like a baby: Mrs. Crater shows how base she is in sacrificing this innocent to a man she hardly knows, simply to marry her daughter off and have a man on the premises to do the work she cannot do. She is not moving in the direction of redemption.
Don't Lucynell look pretty? Looks like a baby doll.
Tom Shiftlet is a man who is in need of salvation and redemption. He seems to be decent in the work he does when he agrees to stay: he helps fix a roof, the pig trough, etc. He teaches Lucynell her first word: bird. It is not until Mrs. Crater squeezes out what tenuous goodness there is within him with her devastating words that Tom Shiftlet (as his name seems to denote) "shifts"—he loses his faith and becomes something that even he is ashamed of. Mrs. Crater confronts him with harsh words to force the deal about the marriage:
...you'd be getting a permanent house...and the most innocent girl in the world. You don't need no money. Lemme tell you something: there ain't any place in the world for a poor disabled friendless drifting man.
These words pain him, and the simile referring to buzzards brings a vision of "death"— perhaps the death of his faith.
The ugly words settled in Mr. Shiftlet's head like a group of buzzards in the top of a tree.
Mr. Shiftlet is aware that a man is made of body and spirit. He knows that life is not only about money. His life a is struggle to find a place in the world because his is not "whole," physically or spiritually. Mrs. Crater's offer daughter and car, in exchange for his freedom, become a temptation, and when she sweetens the deal with money, he accepts. They travel into town and Shiftlet and Lucynell are married. The couple leaves, driving to Mobile—Shiftlet's destination.
They stop at a diner, and when Lucynell falls asleep at the counter, he abandons her there. As he continues on the trip, he is filled with a sense of shame. He realizes he has become as sinful as the world that surrounds him.
Although he could have found salvation in settling down on the Crater's farm, Tom allows Mrs. Crater's manipulation and her harsh words to define who he is. In continuing his trip to Mobile, we sense he has left behind his opportunity for salvation in turning his back on Lucynell and what he believes to be right.