Personally, I did not fully understand what the film was trying to say with the editing and montage, but I did get the sense that it was supposed to invoke feelings of longing, sadness, passion, etc. When she reads the letter, we see that she is affected in some way, but I was not sure of the contents of the letter until Will told us in class that is was her lover breaking up with her.
The scenes of the lake and fog definitely feel like sadness, but I didn’t get the feeling of nature ‘losing its density and unity’ like the director had stated.