"Come Up from the Fields Father" is a poem about how a mother receives a letter saying that her husband has died. The poem starts out with the daughter enjoying the countryside.
"There Will Come Soft Rains" is a poem about Earth being turned into a wasteland after a nuclear war. Animals slowly die but other things still go on.
The role of nature as described in the two poems is that it sets an expectation of something good. The natural world will bring us bad things and will continue on without us.
