Four lines, each built the same way, and together they form a circle. The body limits the mind, the mind limits the universe, the universe limits language, and language limits the body again. There is no exit. Wherever you start, you end up back where you began.
The speaker seems to feel boxed in, though the tone is calm rather than angry. Nothing is complained about; the facts are simply stated, one after another. That flat, repeated phrasing makes the poem feel like a lock clicking shut four times. It also mimics its own message: the poem can't say anything new because its language keeps returning to the same words.
The mood is quiet and a little dizzying. You might read it as a sad acceptance of human smallness, or as a puzzle about how everything we are depends on everything else. The poem doesn't tell you which, and that open question is part of what lingers.