Human perception
The poem's main interest is in how our own subjective senses define our experience of the world. To have a "mind of winter" would be to strip away all extra connotations and emotions that we usually attach to our environment; when we try to imagine doing so, we see that our experience of winter is completely defined by these connotations. The practical application of this idea is: winter is only miserable, or beautiful, because our imagination makes it so. We can see the ice-glittering trees as beautiful, or feel despair at the barren wind; either way, these experiences are a product of the emotional reactions that we bring to our perception of the world.
Reality vs. nothingness
Closely related to the theme of human perception, reality and nothingness are blurred together in this poem. To strip away the imagination through which we perceive nature would be to confront the void. The poem asks whether this kind of detachment is possible: whether, through mental exercise, we can understand the trees and snow and ourselves as a blank slate of physical 'reality,' wiped of all subjectivity. This may be impossible, as emotional projection is inherent to human nature. Perhaps 'reality' as we know it could not even exist separate from the human imagination. Nevertheless, Stevens invites us to contemplate that nothingness without fear, and remind ourselves that, at any given time, we are constantly projecting our own point of view onto the physical world around us.
Natural unity
The poem's landscape blurs together into a unified whole that ultimately encompasses the observer as well. This is partly a product of the snow, as winter has the power to cover everything with a blanket of uniformity, and partly due to the poem's thought experiment of attempting to strip nature of human subjectivity. Though the pines, junipers, and spruces are at first differentiated, soon the "sound of the wind" and leaves becomes the same as "the sound of the land," the same wind in the "same bare place" as the listener. All the landscape and its elements are one in winter, and with his subjective emotions subdued, the listener is also absorbed into this natural unity, perhaps implying that the emptiness is also peaceful.
