"But I have won in this: I've never excused my failures by sneering at my aspirations, by pretending to have gone beyond them. I do not admit that Main Street is as beautiful as it should be! I do not admit that Gopher Prairie is greater or more generous than Europe! I do not admit that dish-washing is enough to satisfy all women! I may not have fought the good fight, but I have kept the faith."
"Sure. You bet you have," said Kennicott. "Well, good night. Sort of feels to me like it might snow tomorrow. Have to be thinking about putting up the storm-windows pretty soon. Say, did you notice whether the girl put that screw-driver back?" (39.8.11)
Even though she ends up returning to Gopher Prairie at the end of the novel, Carol Kennicott vows that she will never surrender to the simple-mindedness of the town and its people. She makes a passionate speech about how she will go on think of new ways to make the town more beautiful, even if she knows that nothing will ever come of these thoughts. In her words, she may not fight the fight, but she'll keep the faith by refusing to let herself be convinced that the town and its people are fine just the way they are.
Of course, Lewis can't help but give the last word in the book to Will Kennicott. He hears Carol's speech and basically says, "Yeah, yeah. That's really great, Carol. But now I'm going to go back to thinking about all the boring daily stuff I always think about." In other words, Will's never going to really change, no matter what Carol says or does. The same goes for Gopher Prairie itself: it's probably never going to really change.
And that's where Lewis leaves us—right back where we started.