The first stanza of the poem sets up the theme of unreality: this is not a realistic vision of the world but rather an idealized and romanticized portrayal of the life this shepherd promises to his love. This unrealistic, romantic landscape creates an idyllic tone that pervades all of the metaphors in the poem.
Notice that the speaker uses that word “lamb” to describe his flock rather than using the word “sheep.” Lambs are baby sheep, and their name has been adopted as an adjective to describe people with a meek, gentle or innocent disposition. It is also used to describe members of a church congregation in the Christian tradition. The use of this word adds to the edenic or idyllic tone of the poem: down to the animals that these shepherds raise, everything is innocent, gentle, and simple.
The birds’ ability to sing “madrigals” together suggests an almost supernatural ability to sing complex music. This type of melodious birdsong personifies the creatures and adds to the dream-like, pastoral landscape of the setting.
