The difference between Christian ethics and non-Christian ethics has not been made perfectly clear at this point unless we dwell on the fact that even in its original perfect condition the moral consciousness of man was derivative and not the ultimate source of information as to what is good. Man was in the nature of the case finite. Hence his moral consciousness too was finite and as such had to live by revelation. Man’s moral thought as well as the other aspects of his thought had to be receptively reconstructive.
This then is the most basic and fundamental difference between Christian and non-Christian epistemology, as far as it has a direct bearing upon questions of ethics, that in the case of non-Christian thought man’s moral activity is thought of as creatively constructive while in Christian thought man’s moral activity is thought of as being receptively reconstructive. According to whom man is responsible and from whom he has received his conception of the good, while according to Christian thought God is the infinite moral personality who reveals to man the true nature of morality.
It is necessary, however, to think of this revelation of God to man as originally internal as well as external. Man found in his own makeup, in his own moral nature, an understanding of and a love for that which is good. His own nature was revelational of the will of God. But while thus revelational of the will of God, man’s nature, even in paradise, was never meant to function by itself. It was at once supplemented by the supernatural, external and positive expression of God’s will as its correlative. Only thus can we see how basic is the difference between the Christian and the non-Christian view of the moral nature of man in relation to ethical questions.
(Van Til, The Defense of the Faith, 53)