Bonta starts with something small and a little eerie: knotholes lying on the ground like empty eye sockets. From there he becomes almost a patient teacher, explaining how a tree protects itself. Where a branch meets the trunk, the tree builds its hardest wood, and inside the trunk it forms a spear-shaped core that holds off rot long after the branch is gone. That core is the knot.
The tone is calm and factual, full of arborists' terms, but the ending turns it into something more personal. Calling knots "hard pills" the tree couldn't dissolve suggests they are kept-in hurts, and the last lines widen this into a general truth: every time the tree reaches toward the sun, a "no" forms inside, "firm & sharp / & pointed inward." The speaker seems quietly admiring and a little wary. Growth and openness, the poem implies, always leave behind some hardened defense. The mood is thoughtful, still, and slightly sombre.