Many deists affirm that religious duty consists in doing justice and loving mercy, that the heart of true religion is right conduct toward one's fellow human beings rather than creed, ritual, or ceremony. On this view a rational religion issues chiefly in morality: honesty, benevolence, fairness, and compassion. The formulation echoes the ancient prophetic call to do justice and love mercy, which deists could embrace as an expression of the natural moral law they held to be knowable by reason and binding on all.
The formulation directly echoes the prophet Micah's summary of true religious duty: "to do justice, and to love mercy, and to walk humbly with your God" (Micah 6:8), a text deists could read as confirming, from within scripture itself, that ethical conduct rather than ceremonial observance was religion's real substance. Benjamin Franklin, whose personal religious views leaned strongly deist, expressed a version of this ethic in his autobiography, describing his mature conviction that "the most acceptable service of God" was "doing good to man" rather than formal worship, and organising his own personal moral improvement scheme around a list of practical virtues rather than doctrinal creed, a characteristically deist reduction of religion to ethical self-cultivation.