Matthew's haiku moves quickly, in just three short lines, from a scene of nature to a quiet feeling of relief. The first two lines paint a picture: movement among trees, and willows whispering as the wind passes through them. The spelling "wispering" is a small twist. It seems to blend "whispering" with "wisp," so the sound feels light and thin, like something barely there. Whether that was intended or a slip, it suits the gentle image.
The last line changes direction. "Hard nights left behind" tells us the speaker has been through difficult times, though the poem doesn't say what kind. Judging by the imagery, the dancing trees and soft wind seem to mirror a lighter state of mind, as if the speaker is moving forward and the world is moving with them.
The mood is calm, airy, and quietly hopeful. Nothing is shouted or explained. The poem simply lets the breeze and the willows suggest that the worst has passed and that some peace has arrived.