At its heart, “Knowledge” is about letting go. The speaker has realized that passion cannot warm a body once it is in the grave, and that even treasure eventually breaks. These are old, painful truths, but the poem does not rage against them. Instead, the speaker seems to say: now that I know this, I will lie still and pay attention to something calmer and more lasting. The trees make a long shadow and a light sound as wind moves through them. That simple image becomes a quiet lesson in acceptance. The mood is not despairing; it is meditative, a little mournful, but mostly peaceful. The speaker trades the heat of wanting for the cool patience of observing nature, finding rest in how the natural world goes on without needing to possess or keep anything.
Knowledge — Summary
Now that I know How passion warms little Of flesh in the mould, And treasure is brittle, —
I'll lie here and learn How, over their ground, Trees make a long shadow And a light sound.