In "On His Blindness," the writer, John Milton, talks openly about losing his eyesight, an event which began in the 1640s as a result of his heavy workload. Milton was completely blind by 1652.
In the first few lines of the poem, Milton reflects on losing his sight before he reached middle age and describes how his world has become totally dark. For Milton, this is particularly concerning because he now wonders how he will serve God, his master. Specifically, he wonders if God expects him to do "day-labour," everyday tasks, while he is in darkness.
As Milton ponders this question, "Patience," personified here as a living person, interjects his thoughts and softly reminds him that God does not need Milton to do anything. In fact, Patience tells him that the best way to serve God is just accept life for what it is since this is God's will.
Finally, Milton is also reminded that God has plenty of people to run around and carry out his errands. More importantly, Milton should wait patiently and trust that God will know the best way to use him (and his blindness).