What man has made of man.
Through primrose tufts, in that green bower,
The periwinkle trailed its wreaths;
And 'tis my faith that every flower
Enjoys the air it breathes.
The birds around me hopped and played,
Their thoughts I cannot measure:—
But the least motion which they made
It seemed a thrill of pleasure.
The budding twigs spread out their fan,
To catch the breezy air;
And I must think, do all I can,
That there was pleasure there.
If this belief from heaven be sent,
If such be Nature's holy plan,
Have I not reason to lament
This suggests that the narrator believes the  creatures derive pleasure by simply existing as they naturally are.
Lines Written in Early Spring