Heat starts out as a poem about opposites: one thing gives heat, another gives light, one moves left, the other right. Day and night, black and white, round earth and square blocks. Then it narrows to writing itself, with letters, symbols, ink on paper, and the odd, painful image of ink "bleeding."
From there the poem treats paper as something fragile and almost alive. "Paper people" and "paper cages" suggest that the characters and ideas we put into books can both represent us and trap us. They look "fine and slick and real," but the poem warns that a lit torch will make them peel.
The final stanzas turn to fire, which curls and licks its way through the page. The speaker seems fascinated and a little mournful at once. The mood is quiet, watchful, and ominous, as if the poem wants us to admire how much ink and paper can create while remembering how easily it all turns to ash.