Men will not understand that when they fulfill their duties to men, they fulfill thereby God’s commandments; that they are consequently always in the service of God, as long as their actions are moral, and that it is absolutely impossible to serve God otherwise.

Immanuel Kant (1724–1804) German philosopher

(Attributed)
    (Source)

Quoted in Karl Hillebrand, Lectures on German Thought, Lecture 5 "The Triumvirate of Goethe, Kant, and Schiller (1787-1800)" (1879)