What are the two main ideas in "There Will Come Soft Rains"?

In this story, Bradbury shows how humans will be the agents of our own destruction. The narrator describes a house that does everything for its owners, all on its own. It cooks, it cleans, it reads poetry, and it even has a mechanism designed to put out fires. The narrator explains that this house is the only one still standing in a "city of rubble and ashes [....]. At night the ruined city gave off a radioactive glow which could be seen for miles." Though the house's interior is in ship-shape, kept clean by the robotic mice and automatic sink, its exterior is printed with the silhouettes of its former owners who were, it seems, incinerated by some kind of fiery blast from the now-radioactive town. We are left to assume that the technologies put to use in the house—technologies that will be responsible for its immolation—are to blame for the destruction of the entire city.

Further, Nature is more powerful than we are, and it will recover from the damage we inflict on it after we are gone. Like it says in the poem the house reads to its absent owners, soft rains will come and birds will nest and frogs will sing, and none of them will know of us or what happened to us, and none will care. In fact,

Not one would mind, neither bird nor tree,
If mankind perished utterly;

And Spring herself, when she woke at dawn
Would scarcely know that we were gone.

The humans and their domesticated pet have died, but the rains have come and the drops "tapped on the empty house," proving that Teasdale's predictions can and will come true.

What are the two main ideas in "There Will Come Soft Rains"?

One of the key ideas that Bradbury asserts in “There Will Come Soft Rains” is that the technology we humans increasingly rely on has the potential to cause great destruction, as already evidenced by an allusion to the events of Hiroshima. In the actual use of the atomic bomb, some people were vaporized, leaving “nuclear shadows” where they stood when the bomb hit. This is captured in the description of the outside walls of the house in this story:

The entire west face of the house was black, save for five places. Here the silhouette in paint of a man mowing a lawn. Here, as in a photograph, a woman bent to pick flowers. Still farther over, their images burned on wood in one titanic instant, a small boy, hands flung into the air; higher up, the image of a thrown ball, and opposite him a girl, hands raised to catch a ball which never came down.
The five spots of paint - the man, the woman, the children, the ball - remained. The rest was a thin charcoaled layer.

This family was caught completely unaware of the impending danger as evidenced by their actions reflected in the nuclear shadows. Much like this family, many of us carry on with daily life, unaware that our increasingly complex technologies could devastate us all.

Second, Bradbury shows that humanity is not the most lasting force on the planet. After humans have destroyed each other using technology they created, nature remains. Therefore, perhaps humans would better serve our futures by connecting with a nature which is life-giving (shown in the “soft rains” rather than technology which is ultimately destructive.

What is the main theme of "There Will Come Soft Rains"?

The main message of this story could differ from reader to reader, and the story contains multiple themes. Themes can lead readers toward choosing a particular message, but a story's theme and message are not guaranteed to be the same thing. Thematically, there are themes that focus on nature and technology. I could even be convinced that the story has a theme of family as well since it shows a house that once contained a family that spent time together at the table and/or out in the yard together. One message that I like steering students toward is the general belief that technology is inherently beneficial and has the ability to solve all problems. This concept has been referred to as the "Myth of Technology as Protector and Savior." This Bradbury story shows that thinking is flawed. As great as the house's technology was, it couldn't save them from the disaster. Additionally, it was man's technological advances that created the apocalypse in the first place. The takeaway is then that technology is both beneficial and incredibly dangerous.

What is the main theme of "There Will Come Soft Rains"?

Though he was fascinated with and inspired by technological growth, Ray Bradbury also possessed profound fears about its potentially destructive and dehumanizing effects. In "There Will Come Soft Rains," a 1950 short story inspired by a 1920 Sara Teasdale poem, Bradbury expresses the theme that Nature will outlast anything man can create on Earth. 

Though the fully automated house at the center of the story continues to function for a few days in the absence of its owners (who have apparently perished in a nuclear holocaust, the most destructive force manufactured by mankind), it is brought to its end by elemental forces of Nature. A tree branch, brought down by wind, leads to the ignition of a flammable cleaner, and fire consumes this symbol of man's technological achievement.

Bradbury's story observes that mankind could ultimately bring about its own destruction through war.  Because the world had so recently witnessed the global resonance of the atomic bombs that ended WWII , Bradbury's cautionary tale about the self-annihilating potential of technology was particularly resonant.

Bradbury, Ray. "There Will Come Soft Rains." 1950

What are the important themes in "There Will Come Soft Rains"?

The main theme of "There Will Come Soft Rains" is a critique of technology. The story focuses on a house that does everything for the family that lives in it, from waking them up in the morning and preparing breakfast to later setting up their card table. This might look appealing, except that we soon discover the family and the civilization around the house have been destroyed by what appears to have been a nuclear war. Technology, we find, was not really a servant of humans, but an out-of-control, destructive force. Bradbury is warning us to be careful about an unthinking embrace of technology.

Second, the story shows nature triumphing over technology. The house quickly reverts to a state of nature as it burns to the ground. A second theme of the story is that nature is, in its quiet way, more powerful than humankind's inventions.

What incidents triggered the events in "There Will Come Soft Rains"?

A typical plot sequence begins with the exposition and moves into rising actions. Next comes the story's climax followed by the falling actions and resolution. If this question is asking for what event triggered a narrative about a lone house in a completely empty and destroyed neighborhood, then the likely answer is some kind of nuclear disaster. Readers are not told that it was a nuclear disaster, but there are subtle clues in the story that hint toward this event. The nuclear disaster could have been a nuclear bomb, or the disaster could have resulted from a nearby nuclear reactor exploding. The second option would be similar to what happened in Chernobyl.

The first clue that hints at a cataclysmic nuclear event appears when the narrator tells us that it is ten in the morning. We are told that the house is the only house left standing amid "rubble and ashes." The ash is important because it hints at everything having been incinerated. The paragraph finishes by telling readers that a "radioactive glow" could be seen at night.

The house stood alone in a city of rubble and ashes. This was the one house left standing. At night the ruined city gave off a radioactive glow which could be seen for miles.

The very next paragraph tells readers that silhouettes of people have been burned into the side of the house. This is something that was reported to have happened after the bombs were dropped on Hiroshima and Nagasaki to end World War II.

The nuclear event incinerated the people, and that is why they are not around to answer the house. Had the people been around, it is quite possible that the fire would have been put out. At the very least, the house would have had help in fighting the blaze.