At this point I may interject that when I thus emphasize the absolute antithesis, I am not denying or even for a moment forgetting the doctrine of common grace. That doctrine does not militate against the doctrine of the absolute antithesis, but here as elsewhere confirms it. Common grace does no overlook ultimate differences. Nor does it, when correctly understood, in any way, tone down those ultimate differences. On the contrary, common grace helps to point out that things which look alike are not ultimately alike. Common grace points specifically to the fact that similarities between the people of God and the people of this world are but proximate similarities and that these proximate similarities play before the background of ultimate differences. If people do not believe in common grace or do not know what it means, they are likely to raise proximate similarities to ultimate similarities or to raise proximate difference to ultimate differences with the result that the absolute differences are toned down. It is this which has often taken place in Non-Reformed Churches. There it has been thought that religions is a condiment that may be added to the otherwise neutral territories of life. Because they did not understand the doctrine of common grace these churches took it for granted that no ultimate difference could be hidden behind the statement of a Christian that two time two are four and a statement of non-Christian that two times two are four.
Now the fact that two times two are four does not mean the same thing to you as a believer and to someone else as an unbeliever. When you think of two times two as four, you connect this fact with numerical law, you must connect numerical law with all law. The question you face, then, is whether law exists in its own right or is an expression of the will and nature of God. Thus the fact that two times two are four enables you to implicate yourself more deeply into the nature and will of God. On the other hand, when an unbeliever says that two times two are four, he will also be led to connect this fact with the whole idea of law; but he will regard this law as independent of God. Thus the fact that two times two are four enables him, so he thinks, to get farther way from God. That fact will place the unbeliever before a whole sea of open possibilities in which he may seek to realize his life away from God. And it is the basic difference between what “two times two are four” means to the believer and what it means to the unbeliever that the doctrine of common grace has helped us to see. It has enabled us to focus our attention upon the antithesis without fearing that we are doing injustice to any of the facts that surround us.
Cornelius Van Til, “Antitheses in Education,” Foundations of Christian Education: Addresses to Christian Teachers, ed. Dennis E. Johnson [Phillipsburg: Presbyterian and Reformed Publishing Company, 1990], 7-8