This thing, called conscience, is in everyone; there is no man without it. You may as well suppose a man without an understanding as without a conscience; and without a power to know anything, as without a power to reflect upon himself. Every reasonable soul, being capable both of sin and grace, is endued with a power of reflecting upon itself, that sin may be condemned and grace may be approved. All are called upon to “consider their ways” (Haggai 1:5, 7), but to take our own ways into consideration is the work of conscience; conscience therefore is in all.
(Heaven Upon Earth)