In February of 1652, the English poet John Milton went completely blind. Many great artists have suffered blindness, but the twist in Milton's case is that he went blind before he wrote his best works, including the immortal epic poem Paradise Lost. Milton had written a few great poems before 1652, such as the elegy "Lycidas." But he was not a famous poet by this point.
In fact, Milton was more famous as a servant of the government of Oliver Cromwell, the "Lord Protector" of England during the period between the kings Charles I and Charles II. Without going too far into English history, we'll just point out that from the years 1649 to 1660, there was no monarchy. Charles I had been beheaded, and Cromwell turned the government into a republican commonwealth, which is to say, not a monarchy. Milton was a Puritan, and so was Cromwell. The 17th century Puritans believed that the Church of England needed to be reformed to create more distance from the elaborate ceremonies and power structures of Catholicism and the Pope. They wanted to boil Christianity down to the basics of "pure" piety and morality. Thus, Milton was a big-time supporter of the commonwealth government, and he used his incredible powers of persuasion on behalf of Puritan rule in essays published in pamphlets.
But, like we said, Milton went blind a few years after the Puritans gained power, and in this sonnet he worries about how he can serve God even with this condition. Many scholars date the poem to 1655 (source). When reading this poem, you have to keep in mind that Milton is not just using false modesty here, because he had not written the works that would cement his reputation. Hearing the author of Paradise Lost say, "I haven't accomplished all the stuff I wanted to!" would be like Tiger Woods complaining that his life was wasted because he had never won the world Sudoku championship. But that's not what Milton is doing in this sonnet – his "talent" at this point was still unproven.
Milton's blindness has become something of a myth. Some people think that Milton dictated all of Paradise Lost to his three daughters. And at least one scholar has suggested that he drove his daughters out of his house by making them read to him in languages they couldn't even understand (source).
When John Milton went blind, he must have felt like modern athletes feel when they suffer a career-ending injury. You spend your whole life working toward a goal, pour your heart and soul into practicing, and then some uncontrollable event or freak accident puts you back in the shoes of a regular guy. In the movie Friday Night Lights, the star high school running back Boobie Miles injures his knee and loses the chance to play for a state championship and earn a college scholarship. Things like this happen to people all the time, we just don't normally hear about them. The myth is that if you work hard enough, you can achieve anything. But, as many people have discovered, while you certainly can't achieve great things without working hard, the hard work is no guarantee.
John Milton's life plan was to be of service to God. He felt he could best achieve this goal by using his intelligence and especially his writing. But back when Milton was alive, it was very hard to write when you had no vision. He was entirely dependent on other people to write down his work and read to him. Fortunately, Milton's blindness was not as crippling as he thought it would be, and he eventually adapted to the condition enough to write some of the world's great works of literature.
This poem shows, though, that outcome was far from a sure thing. This sonnet puts us in the shoes of someone with enormous talent who must suddenly accept a new purpose in life. He goes from being a mover-and-shaker to being someone who merely "stands and waits" on God.