What is the most important moral lesson in "There Will Come Soft Rains"?
I think that what you are asking is whether or not There Will Come Soft Rains has a moral to it?
Yes, yes it does!
The story by Bradbury as well as the poem by Teasdale (both with the same title) teaches humans that technology, while we love it and depend upon it, can be our ultimate downfall unless we are careful.
Technology is great in the story and makes life for the family very easy--the house cooks them breakfast, entertains the children and keeps intruders out so the family can stay safe.
However, this same technology when used for the wrong reasons ends humanity as we currently know it.
We can move forward with what we know and make life easier, but we have to be cautious that we do not misuse our new discoveries.
This idea is very relevant for today--Obama is allowing stem cell research--imagine the great things it can do in the right hands and the awful things that can happen if humans misuse it.