A grown speaker remembers climbing a huge oak as a boy. The climb is physical and painful, with scraped shins and torn fingertips, but it also seems to cure his self-doubt. He is driven by a puzzle: why do the other trees pull away from the oak, and what is the barrier between them?
At the top, he expects some kind of revelation, and the poem tells us what he doesn't find: God, inner peace, a neat reflection of himself. Instead there is a nest of five birds that simply fly off into the sun, quietly and without fuss. The boy has to climb back down and start over.
The mood is reflective, a little wistful, and honest about disappointment. The repeated line about the barrier returns at the end with a sharper question: is the barrier the oak's, or his own? The poem leaves that unanswered, which makes the ending feel unsettled but true.