Why I do it:
General revelation also has a certain value for the Christian religion. Not that it provides us with a religio naturalis, which is quite sufficient in itself and therefore renders all supernatural revelation superfluous. Such a natural religion does not exist, and is in fact impossible. Neither can it be said that the Christian derives his knowledge of God first of all from general revelation, and then supplements this with the knowledge of Christ. He derives his theological knowledge of God from special revelation only; this is his principium unicum. Yet there is a close relation between the two. Special revelation has incorporated, corrected, and interpreted general revelation. And now the Christian theologian takes his stand on the Word of God, and from that point of vantage also contemplates nature and history. He reads God's revelation with the eye of faith and in the light of God's Word, and for that very reason is able to see God's hand in nature, and His footsteps in history. He sees God in everything round about him, and is thereby lead to a proper appreciation of the world. Moreover, general revelation offers the Christian a basis, on which he can meet and argue with unbelievers. The light of the Logos that lighteth every man is also a bond that unites all men. The whole creation testifies with many voices that man is created in the image of God, and therefore cannot find rest except in God. Finally, it is also due to God's general revelation that His special revelation is not, as it were, suspended in the air, but touches the life of the world at every point. It maintains the connection between nature and grace, between the world and the kingdom of God, between the natural and the moral order, between creation and re-creation.
(Berkhof, Introductory Volume to Systematic Theology, in Systematic Theology, pp. 131-132.)
