Basic moral intuitions such as “It is wrong to murder” or “It is right to be loving, truthful, courageous, and compassionate” testify to the truth of objective moral values. These values appear to stand as distinct from, and independent of, the human mind and will. In other words, they are discovered, not invented.
But what accounts for the existence of objective, universal, unchanging moral principles? What guarantees their validity? And what is their source and foundation?
Objective moral values are logically incompatible with all forms of ethical relativism, including naturalistic, atheistic, evolutionary theory. Ethical relativism is incoherent and cannot serve as an acceptable moral theory. In the absence of a morally perfect, personal God morality can only be conventional, arbitrary, and subjective in nature.
Objective ethical principles do exist, but they cannot exist in a metaphysical vacuum. What is morally good (ethical) cannot be separated from what is real (metaphysical) and what is true (epistemological). But atheism has no foundation upon which to ground man’s conscious awareness of moral obligation. Without God, objective moral values have no metaphysical anchor and thus cannot be accounted for.
Unlike secular attempts to account for morality, the ethics of Christian theism are grounded in the morally perfect nature of God who has specifically revealed his will to mankind. God is therefore the source and foundation for objective moral values.
— Kenneth Richard Samples, from Without a Doubt, kindle location 190