The effect of the couplets in both “The Author to Her Book” and “A Hymn to the Evening” is that they allow a poet to link lines of poetry together using sound.
Couplets, which consist of two lines of verse that typically rhyme, create a rhythmic and cohesive structure. This not only enhances the musicality of the poem but also helps to draw connections between ideas and themes explored within the lines. The use of couplets can also create a sense of completeness and closure within the individual units of the poem.