Two short stanzas set up a quiet contrast. In the first, a crow passes overhead, and the speaker is sure it "must call." The bird doesn't need a reason or a decision. Calling is simply what crows do, and the word "without question" makes that certainty feel almost enviable.
The second stanza turns inward. The speaker has "scratched so much / for want of a purpose." The image of scratching suggests restless, small, repeated effort, like a hen in dirt or someone doodling or fiddling to fill time. Set beside the crow, the speaker seems to lack that natural sense of what they're for. The title, "Idle," fits this: busy hands, but nothing driving them.
The mood is wry and a little wistful rather than despairing. There's no big complaint here, just a plain admission, made in a few spare words. The poem leaves us with the feeling of watching something live fully as itself while wondering what our own calling might be.