This is perhaps one of John Milton's most famous poetic works after his epic Paradise Lost. One of the fascinating aspects of his life is that he actually went blind in his middle age, and this is a sonnet that considers this tragedy and tries to find a way of accepting what happened.
The sonnet begins with the speaker grieving for his lost sight and also expressing the fear that because of his blindness, he will never be able to use his abilities as he had hoped. However, comfort is found in the idea that patient endurance and bearing this difficulty with fortitude as he remains open to serving God will advance the divine plan as much as achieving the exploits he had imagined that he could have achieved with his sight. Note what he says:
God doth not need
Either man's work or His own gifts. Who best
Bear His mild yoke, they serve Him best.
The sonnet thus ends on a note of optimism and hope as the speaker becomes reconciled to his state.