Who said or wrote'They also serve who only stand and wait'?

The phrase "They also serve who only stand and wait" was written by John Milton in his poem "On His Blindness." The line reflects the idea that those who are patient and endure hardship also contribute to the greater good, even if they are not actively engaged in visible deeds. Milton, who became blind later in life, expressed this sentiment as a way to convey the value of patience and service in various forms.