Comment on the structure of the poem "On His Blindness."

Milton's poem "On His Blindness" was first published in 1673, twenty-one years after the poet lost his sight completely. The poem is written as a Petrarchan sonnet, which means that a problem is posed in the first eight lines, or octet, and a solution is proposed in the final six lines, or sestet.
The problem posed in the octet is that the speaker fears that he will not be able to serve God now that he has lost his sight. He needs his sight to be a writer, and to praise God through his writing. The speaker asks himself, "Doth God exact day-labour, light denied?" In other words, the speaker worries that God will demand, or exact work from him that he is no longer able to produce because he is now "light denied."
In the octet, the speaker offers his own solution to the problem when he reminds himself that God is pleased not necessarily by the works of man, but rather by those "who best bear (their) mild yoke." In other words, God is pleased when people bear their burdens with grace and patience, "who only stand and wait." The speaker is thus satisfied, at the end of the poem, that he serves God well simply by bearing his blindness with grace and patience.