In the first place there is a basic difference concerning the nature of revelation. For Calvin, revelation is always and everywhere clear. The facts of natural revelation, both within and about man, are so clearly revelatory of God that he who runs may read. The indicia divinitatis (marks of divinity) of Scripture are equally clear. In fact, the revelation of God to man is so clear that no man can help but know God. Thus man is from the beginning in contact with the truth. Moreover, he cannot separate the existence of God from the character of God. The intelligibility of anything, for man, presupposes the existence of God—the God whose nature and character are delineated in God’s revelation, found both in nature and in Scripture. It is this God—the only God—whom all men, of necessity “know.”
Over against this idea of revelation, as clearly and exclusively based upon, and expressive of, the idea of the Creator-creature distinction, stands that of Aquinas. According to Aquinas the revelation of God to man is not inherently clear. As finite man lives on the verge of non-being; 14 and as such a mixture, man’s knowledge is derived from the senses. Man is also, therefore, enmeshed in an environment which is not exclusively determined by the plan of God, but rather a combination of the forces of God and of chaos. 15 Accordingly, Aquinas thinks that man can intelligently discuss the question of the existence of God without at the same time presupposing the nature of God as revealed in Scripture. Thus the attitude of doubt with respect to the existence of God is assumed to be legitimate. Ignorance is not basically culpable.
Involved in this original separation of the existence and the nature of God is the idea that for man, the nature of God is not exclusively determined by the revelation of God. The nature of God is, in part, determined by man himself.
It is thus that the scholastic notion of natural theology is born. If man, without special revelation, partly determines the nature of God, then this nature of God is, to an extent, defined by the supposed demands of logic and fact, as man knows these independently of the revelation of God. Thus the distinction between the revelation of God to man and the interpretation of this revelation by man is obscured. Natural revelation then tends to be identified with natural theology. This idea of natural theology assumes that without Scripture and the testimony of the Spirit men generally can have a measure of morally and spiritually acceptable knowledge of God. It assumes that there can be an interpretation of the natural revelation of God with which both believers and unbelievers are in basic agreement.
The difference between the knowledge of the Christian and the knowledge of the non- Christian consists, then, primarily by the former being more comprehensive than the latter. The Christian adds to his knowledge of facts obtained by his own empirical research without reference to Scripture, the information about these facts that he gets from supernatural revelation. On the Thomistic basis the difference between the knowledge of the Christian and the knowledge of the non-Christian is primarily quantitative. To be sure, according to Thomas, sin has wounded the natural capacities of man. Accordingly the supernatural must, to some extent, be remedial as well as supplementative. This fact, however, does not change the fact that for Thomas supernatural revelation is primarily supplementative.
Aquinas thinks of the position of Calvin as being rationalistic because he holds that man unavoidably, by virtue of his innate knowledge of God, is in contact with the truth. If all men do of necessity know God, Aquinas would reason, then how could they be responsible for seeking out God in the world? How could they be responsible creatures in the sight of God? Aquinas therefore insists that man is only potentially, and not necessarily, in contact with the truth about God.
On the other hand, Aquinas thinks of Calvin’s position as being irrationalistic because he says that none but the elect, after the entrance of sin, can be said to have any morally or spiritually acceptable knowledge of God. Aquinas would say that all men have this truth potentially, but not all realize the full development of this knowledge. Aquinas is concerned, therefore, about cultivation, while Calvin is concerned about implantation of the grace and knowledge of God, and only after that about its implementation.
Calvin thinks of the position of Aquinas as being irrationalistic, because it is not clearly and exclusively from the outset based upon the distinction between God as Creator and man as creature. Any position that is clearly based upon this distinction, Calvin would say, must regard the image of God in man as implying the idea of inherent knowledge of God. It is only this inherent and unavoidable content of human knowledge that makes it possible to avoid scepticism and to hold man responsible for sin. Without this idea of the unavoidability of the knowledge of God on the part of man, it is always possible for man to make an excuse for not knowing God. Herein is the irrationalism of Aquinas.
Secondly, Calvin thinks of Aquinas’ position as being rationalistic because it assigns to the mind of man the ability to determine to some extent the nature of God apart from the contents of divine revelation. If the knowledge of God’s nature is not from the outset given with the knowledge of man’s nature as the creation of God, then it is up to man to determine the nature of both God and man for himself apart from revelation. Man is therefore left to his own devices and determines a “way which seems right unto man.”
In the third place, man is also responsible, to some extent, for determining the nature of sin. Thus sin cannot, on Aquinas’ position, be “want of conformity to, or transgression, the law of God” which God has, on the basis of his nature, given to man, but is rather the transgression of that which is “fight in his own eyes.” The only revelation of himself and his laws which God may give man, therefore, must be in terms of what man has by his own logic and experience already said about God, religion, and morality. God must listen to man before man listens to God.
To be sure, Aquinas does not carry out this point of view with such consistency. But, since he assigns to the mind of man, some measure of ability to determine the nature of both God and man, apart from being taught of God through Scripture and the testimony of the Spirit, God is no longer the sovereign God of mankind.
(Van Til, The Reformed Pastor and Modern Thought)