What is the tone of "Autumn" as set by the last two lines of the first stanza?

"Autumn" by Ron Campbell heralds the coming of winter with its vivid imagery of the passage of autumn into the world of winter. Winter’s strength is exposed in the last two lines of the first stanza, “That kills all forms of life and feeling/ Save what is pure and will survive.”
These two lines set the tone, as they speak to winter’s ability to destroy the weak yet save what can endure its killing forces--the survival of the fittest. This is a tone of both foreboding and hope. As the poem progresses, the the speaker's admiration for the season of autumn as a precursor to winter is uncovered. His words reflect the things that die, such as the olive branches and grapevines, but tell how these things are transformed into the warm winter fire and the glass of red wine made from the grapes on those vines.