The theme of fanaticism that is present in Chapter 22 of The Grapes of Wrath in the form of Mrs. Sandry is one of the strongest negative comments that Steinbeck makes about the nature of organized religion. The encounter with Mrs. Sandry shows how Steinbeck believes that the failure intrinsic to organized religion is its propensity to move too close to fanaticism. In Steinbeck's mind, this warrants rejection because it goes against the fundamental grain of hope that he views as intrinsic to the characters he depicts.
Mrs. Sandry is shown to be a fanatic zealot. Her introduction in Chapter 22 is reflective of this. The first time she is seen is in a warning to Rose of Sharon about how sinful behavior will kill her unborn child. Mrs. Sandry talks to Rose of Sharon about the "dancin’ an’ huggin’" and in her discussion with Ma Joad, the woman says, "I can see your black soul a-burnin'. I see that innocent child in that there girl's belly a-burnin'." In the name of religious fervor, Mrs. Sandry is willing to voice despair and condemnation of many, resulting in little room for progressive change. For Steinbeck, this condemnation and fear- mongering is the fanaticism that goes against the hope that people like the Joads display.
Steinbeck is voicing a position that suggests the real failure of organized religion lies in its fanatic appeal to create arbitrary distinctions of "sinners" and "saints." Mrs. Sandry is in stark contrast to Jim Casy and his belief of how there "is only what people do" in terms of understanding redemption and condemnation. Jim Casy leaves the institution of the church because of this understanding. It is for this reason that Steinbeck views someone like Casy is viewed with admiration and optimism. It is also the same reason that he views someone like Mrs. Sandry with contempt and scorn. For all her religious fervor, Mrs. Sandry is not doing anything to uplift the condition of those who suffer. In this, Steinbeck offers a critique of organized religion, clearly suggesting that what is done in terms of action is more meaningful than what is said. In Mrs. Sandry's actions in chapter 22, Steinbeck's beliefs about organized religion becomes clear.