John Quincy Adams, the sixth president of the United States and the son of John Adams, the second president said that Christianity produced the public morality necessary for civil freedom because God alone affects the heart:
Human legislators can undertake only to prescribe the actions of men: they acknowledge their inability to govern and direct the sentiments of the heart; the very law styles it a rule of civil conduct, not of internal principles. . . . It is one of the greatest marks of Divine favor . . . that the Legislator gave them rules not only of action but for the government of the heart.
And he pointed to three different beliefs he said were foundational to morality:
Three points of doctrine, the belief of which, forms the foundation of all morality. The first is the existence of a God; the second is the immortality of the human soul; and the third is a future state of rewards and punishments. Suppose it possible for a man to disbelieve either of these articles of faith and that man will have no conscience, he will have no other law than that of the tiger or the shark; the law of man may bind him in chains or may put him to death, but they never can make him wise, virtuous, or happy.