The form originated in Italy, particularly under the influence of Petrarch. Milton and Wordsworth are the two principal practitioners of this form in English. Very often the sestet will respond to a problem raised in the octave, so that the two parts of the poem seem to work in dialogue. Sometimes a poet like Sidney or Shakespeare will write an English sonnet that will thematically follow the Italian pattern of octave and sestet. The first sonnet from Astrophil and Stella is a good example.
Sonnets are difficult to read.
The language is complex, and the poet tries to compress as much information into the fourteen lines as possible. However, once we recognize that the poets use the form to indicate the structure of their thoughts, the poems become easier to read. New metaphors and new ideas are often introduced with each quatrain. We can expect some kind of summary or final statement in the couplet. We should also watch for the problem-response pattern between the first eight lines and the last six.