This story is set in the future (it was published in 1950). It is the year 2026 and technology has advanced in two significant ways. First, there is substantial technology to fully automate a house. The house in the story serves as alarm clock, cook, calendar, virtual secretary, gardener, maid, etc. There is also the technology to have weapons of mass destruction (atomic weapons). The family that used to live in this house has been vaporized, along with all the families in the general area and perhaps beyond. However, much of the house has survived the atomic blast and the house continues to function as if the family were still alive and well.
The house schedules everything. Evidently, the house was programmed to recite a poem every night. When the house asks Mrs. McClellan which poem she would like to hear, no one is there to respond. The house selects a poem at random and the selection is "There Will Come Soft Rains" by Sara Teasdale. The poem suggests that if mankind "perished utterly," nature and the remaining creatures would scarcely care or notice that mankind was gone. The phrase is "there will come" and this suggests that sometime in the future, "there will" come a time when humans will annihilate themselves. Or, at least, the suggestion is that there will come a time when humanity will be capable of this. It is a cautionary poem in a cautionary story. This could happen and when it does, the rains will come and nature will be oblivious to the fact that humans are gone. It is a lesson for humans to have some humility and to take serious responsibility for the technology they create.