The speaker is a composer working through the night, and the poem tries to capture what that kind of work feels like from the inside. The opening image, "a fur of instruments," makes sound feel soft, thick and almost alive. The music is not just heard but wears the speaker like a coat, and it seems to break the ear open, as if listening here is a forceful act.
What the speaker is reaching for stays just out of range. It is "something I cannot presently say," something about the simplicity of the sea or a rose touching skin. Both images are plain and physical, which suggests the music is chasing something direct and basic.
The ending is calm and a little strange. The speaker takes light "in a jar," holds a head "full of order," and pictures sleep waiting in green, singing fields. The mood is quiet, absorbed and hopeful, a mix of tired concentration and satisfaction that the work is taking shape.