God will not have his work made manifest by cowards.

Ralph Waldo Emerson (1803-1882) American essayist, lecturer, poet

Essay (1841), “Self-Reliance,” Essays: First Series, No. 2
    (Source)

The "work" being the actualized human being.

Inspired by his reading of Walter Savage Landor in 1833. Preliminary work, including this phrase, is found in Emerson's journal (1833-01-13). passages pulled for this essay were from his lecture "Individualism," last in his course on "The Philosophy of History" (1836–1837), with other passages from the lectures "School," "Genius," and "Duty" in his course on "Human Life" (1838–1839).