One theme of the story is that nature is stronger than man, and we cannot control everything. Another related theme is that sometimes progress is not progress.
The short story is about the reactions of a family to an earthquake. The young narrator notes that "the scariest thing about quakes is that they change the way a fellow looks at the world" (see first link).
Uncle Toby is so flustered by witnessing the draining of a lake that he becomes obsessed, telling the story over and over again with new information he "remembers."
Of course no one believed this new addition to his tale. But he continued to tell his story to anyone who would listen, adding every time a few more details that would make it just a little more exciting and improbable than it had been before. (see first link)
The frailty of Toby demonstrates how fragile the human psyche is. The boy's father's experience works differently. He refuses to be cowed.
[My] father could laugh in the teeth of anything that would try to kill him in the world. (see first link)
It is also true that sometimes progress is not progress. In the end, the whole family engages in an act of defiance by refusing to get upset by the earthquake and then cracks metaphorically with the cracked dish. Finally, they give in and decide to return to what they know and build a brick fence instead of using the electric fence.