The speaker begins by claiming he was content alone—no one was with him, and he was happy—yet even so, a sudden sense of loss interrupts the sunshine. That unexplained disappearance of joy becomes the poem’s central feeling.
He compares the experience to a bird flitting through an empty house. The bird’s movement stirs sad echoes and makes the rooms feel lonely and strange once it leaves. In the final stanza, the speaker admits his heart was fickle while he enjoyed the passing day. A presence—perhaps a person or perhaps a mood—felt estranged by him and went away grieved. The overall mood is quiet, regretful, and slightly eerie: something warm has slipped away, and the speaker is left with the hollow space it occupied.