Point to textual evidence of a theme or controlling idea in "The Hospital Window"
The theme of Dickey's poem is the transience of life.
The speaker of the poem has just left the hospital bedside of his gravely ill father. He imagines that the skyscraper nature of the building from which he exits is akin to the "white rooms" of Heaven, each soul, he imagines, occupying one of the small frames:
Ceremoniously, gravely, and weakly,
Dozens of pale hands are waving
Back, from inside their flames.
Although each "frame" is seemingly the same, the one that his father is behind somehow different; it is "pure" and "bright", the way in which the speaker wants to remember his beloved father.
Pay attention to the line above as each soul exists "inside their flames." This is an allusion to the Catholic concept of the transient time in Purgatory, where it is believed that souls must be cleansed by fire of their sins before entering Heaven.
The souls in the hospital, the speakers father among them, is in his own sort of Purgatory; he is awaiting certain death and the transition from life to death is painful for both father and son.