The speaker has spent the whole morning "busy sitting," a phrase that sounds like a joke at first. Sitting is hardly a job, yet the title, "Occupation," suggests it is exactly what the speaker is occupied with. It could mean being absorbed in thought, in quiet, or simply in stillness.
Then a song arrives and "summons" the speaker, a strong word, as if the music has real pull. But the response is odd. The speaker's eyes are "too out of tune / to look up." Mixing sight with sound is a neat twist: the eyes, worn from staring or drifting, can't match the song's pitch.
The mood is gentle, a little wistful and a little amused. The speaker feels the call of something beautiful but stays where they are, caught between wanting to respond and being too settled, or too tired, to move. The poem leaves us in that suspended moment, listening without looking.