Whatever man knows of God he knows through God's own revelation of Himself either in the realm of nature or in the realm of grace, that is to say, either through God's work of creation and providence or through His holy Book, the Bible. Hence we rightly speak of a natural knowledge of God and of a supernatural or revealed (Christian) knowledge oi God. Had God not revealed Himself, man never would have known Him, since God is the absolute, perfect Personality, who dwells "in the light which no man can approach unto," 1 Tim. 6, 16.
By means of his natural knowledge of God, man knows that there is a personal, eternal, omnipotent Divine Being, who has created this world and still preserves and rules all things and who is holy and just, demanding what is good and punishing what is evil. This natural knowledge of God is mediated to man -
a. By God's created works (ποιήματα θεοῦ, creaturae Dei), which in themselves bear witness to their omnipotent Creator. In Rom. 1, 20 St. Paul attests that, though God Himself is invisible, man nevertheless knows of Him and, in particular, of His personality, eternity, omnipotence, and sovereignty "by the things that are made." That this is true is proved by the testimony of many heathen philosophers, as, for example, by Aristotle and Cicero. Cicero writes (Tuscul. Disput., I, 28): "Deum non vides; tamen Deus agnoscis ex operibus eius." This natural knowledge of God is so certain that the apostle says of all agnostics and atheists, who deny His divine existence and commands, that "they are without excuse." (The cosmological proof of God's existence.)
b. By God's continued operation in the realm of nature and of human history. In Acts 14, 15-17 St. Paul asserts that God "left not Himself without witness, in that He did good and gave rain from heaven and fruitful seasons, filling our hearts with food and gladness." The knowledge which man gains from God's continued self-manifestation in human history is described by the apostle in Acts 17, 26-28, where he declares that God has made and governs all men in such a manner "that they should seek the Lord" and that "in Him we live and move and have our being" in such a way that even the heathen poets have professed: "We are also His offspring." (The historical proof of God's existence.)
c. By the divine Law written in the heart of man. By means of this Law, men "know the judgment of God," Rom. 1, 32, and without the revealed Law "do by nature the things contained in the Law," "their conscience also bearing witness and their thoughts the mean while accusing or else excusing one another," Rom. 2, 14. 15. (The moral proof of God's existence.)
In view of these facts the antitheistic theories held by men are not the results of sound reasoning, but rather the effects of man's perverse, wilful suppression of the natural knowledge of God, which He has implanted into the human heart, Rom. 1, 18. They -do not represent progress in human religious thought, but rather .spiritual and moral decadence.
Atheism denies God's existence, although by nature man has .a distinct knowledge of God, Rom. 1, 19; Ps. 14, 1. Polytheism divides God into many divine entities, although the knowledge which man by nature has of God is monotheistic (Rom. 1, 20: "His -eternal power"). Hylozoism endues matter with life and denies that God is the erlramundane and supramundane Ruler and Judge of men, though by nature man knows "the judgment of God," Rom. 1, 32. Materialism denies the reality of spirit and ignores the distinction between matter and mind, so that there is in materialism no God and no human soul and no immortality, but only persistence of matter and force. Pantheism is the doctrine that God is all and all is God, so that nothing exists outside of God. Deism admits that there is a personal God, who has created the world and has impressed upon it the laws that govern it, but it teaches that after this, God withdrew from the world and left it to the reign of natural laws. Pessimism regards the world and life as essentially evil and holds that the world, if not the worst that it can be, is at least sufficiently evil to be worse than none at all. A theistic evolution denies the existence of God, asserts the eternity -of matter and force, and attributes the development of the cosmos to purely natural forces (Keyser). Theistic evolution holds that God created the primordial material and that evolution has since been His modus operandi in developing it to ita present status. Agnosticism maintains that we cannot know whether there is a God -or not. Positivism teaches that we can know only phenomena, but not noumena, or the essence of things. Hence it is agnostic in regard to God, the soul, and the substance of things.
All these anti-Biblical theories are in opposition to the natural knowledge of God which Holy Scripture very clearly and emphatically ascribes to man, Rom. 1, 19. 20. 32; 2, 14. 15.
The natural knowledge of God is true as far as it goes, Rom. 1, 18, for what it teaches of God's personality, eternity, omnipotence, sovereignty, holiness, and righteousness agrees with revealed religion. Innate (notitia innata) though it is (Rom. 2, 14. 15: "A law unto themselves"; "the work of the Law written in their hearts"), it can nevertheless be expanded and further confirmed (notitia acquisita) by the contemplation of the works and ways of God in nature and history, Acts 17, 27. 28, though it may also be corrupted and changed into error (anti theistic theories) through the moral depravity existing in man, Rom. 1, 18.
The natural knowledge of God is of great benefit to man because it is the foundation of the civil righteousness (iustitia civilis), Rom. 2, 14; Acts 17, 27, of natural man, and the starting-point for the proclamation of the revealed Law by Christian missionaries. Luther rightly declares that, had God not written the Law into man's heart, we would have to preach a long time before man's conscience would be smitten. (St. L., III, 1053.) When St. Paul preached the Word of God to the Athenian philosophers, he began by appealing to their natural knowledge of God, Acts 17, 23-29.
The natural knowledge of God is of great value also because upon the basis of it man constructs the so-called rational proofs for God's existence to combat unbelief. Thus the ontological proof argues from the existence of the idea of God in man to the actuality of His existence. The cosmological proof concludes that the world must have a First Cause back of all the secondary causes that are operative in nature. The teleological proof argues from the design and purpose which are everywhere evident in nature. The moral proof argues from the existence of our moral constitution to the existence of a Supreme Moral Being. The historical proof draws from the history of man the conclusion that there is a divine Ruler who guides all affairs of the world to an end which He has in view. The theological proof argues God's existence from the fact that the idea of God need never be explained to men, since all men in the world know who is meant by that term. Hence the natural knowledge of God must not be underestimated, since God has bestowed it upon man to govern him in His Kingdom of Power (in regno potentiae), holds him accountable for his attitude toward it, Rom. 1, 18-32, and rewards his respecting and obeying it with temporal blessings, Ex. 1, 20. 21.
In spite of all this, however, the natural knowledge of God is not sufficient to secure man's salvation. Quenstedt writes on this point (I, 261): "The natural knowledge of God is not adequate to secure everlasting life, nor ha.B any mortal ever been redeemed, nor can any one ever be redeemed, by it alone," Acts 4, 12; Rom. 10, 17; Mark 16, 15. 16; Gal. 3, 11; Eph. 4, 18; 2, 12; Gal. 4, 8. Doctr. Theol., p. 110 Since the natural knowledge of God does not embrace the Gospel, 1 Cor. 2, 7-10, but only the Law, Rom. 2, 14. 15, its practical result is nothing more than a guilty conscience, Rom. 1, 20; 2, 15, fear of death, Heb. 2, 15, the state of condemnation, Gal. 3, 10, and utter hopelessness, Eph. 2, 12. Man by nature knows that there is a just and holy God, Rom. 1, 21, but not that the eternal demands of His perfect justice have been satisfied by the vicarious satisfaction of Christ, 1 Cor. 1, 21. In addition, while man by nature knows that there is a God, he does not know who this true God is, 1 Cor. 1, 21; Acts 17, 24. 25; Matt. 28, 19. 20.
While man's natural knowledge of God coincides in some points with the supernatural, or revealed, knowledge of God (articuli mixti), the Christian theologian bases all that he teaches of God alone on Holy Scripture, because this is the only divinely appointed source and norm of faith (principium cognoscendi). It alone teaches the precious Gospel-truths of God, by which man is saved (articuli puri). The Lutheran dogmatician Chemnitz writes of this (Loci Theol., I, 22): "The saving knowledge of God, through which we obtain eternal life, is that revealed through the Word, in which God makes known Himself and His will. To this revelation God has bound His Church, which knows, worships, and glorifies God only as He has revealed Himself in this Word, so that in this way the true and only Church of God may be distinguished from all heathen religions." Doctr. Theol., p. 111
The Christian knowledge of God, which we obtain from Holy Scripture, and from no other source, is not only theistic, but also Trinitarian; that is, the Christian believer knows and worships God only as the Holy Trinity, Father, Son, and Holy Ghost, three distinct persons in one inseparable essence. This Christian knowledge of God is not a mere supplement to man's natural knowledge of God, but an entirely new revelation, by which man is enabled to know God truly and fully, Matt. 28, 19. 20; 1 Cor. 8, 4-6, and to worship Him by true faith as his Savior, Is. 41, 14; 42, 5-8; 43,1--3. 10-12; 44,1-8; 45,20--25.
For this reason every Christian description of God must incorporate also the Holy Trinity; that is to say, whenever a Christian theologian describes God, he must describe Him as the one God who is Father, Son, and Holy Ghost. Calov is right when he says (II, 282): "Those who do not include a statement of the three Persons in the description of God do not present that doctrine in a form at all genuine or complete, since without these it does not yet appear who the true God is." Doctr. Theol., p. 117