John Milton's poem 'On His Blindness' reflects his struggles with blindness and the fear of not fulfilling his potential to serve God. He contemplates the value of his talent for writing, feeling it is wasted due to his condition, while also questioning God's expectations of him in this state. Ultimately, the poem conveys that patience and acceptance of one's circumstances can be a form of service to God, emphasizing that even those who wait and endure still serve a purpose.