Therefore, in reading profane authors, the admirable light of truth displayed in them should remind us, that the human mind, however much fallen and perverted from its original integrity, is still adorned and invested with admirable gifts from its Creator. If we reflect that the Spirit of God is the only fountain of truth, we will be careful, as we would avoid offering insult to him, not to reject or condemn truth wherever it appears. In despising the gifts, we insult the giver. How then can we deny that truth must have beamed on those ancient lawgivers who arranged civil order and discipline with so much equity? Shall we say that the philosophers, in their exquisite researches and skilful description of nature, were blind? Shall we deny the possession of intellect to those who drew up rules of discourse, and taught us to speak in accordance with reason? Shall we say that those who, by the cultivation of the medical art, expended their industry on our behalf were only raving? What shall we say of the mathematical sciences? Shall we deem them to be the dreams of madmen? Nay, we cannot read the writings of the ancients on these subjects without the highest admiration; an admiration which their excellence will not allow us to withhold. But shall we deem anything to be noble and praiseworthy, without tracing it to the hand of God? Far from us be such ingratitude; an ingratitude not chargeable even on heathen poets, who acknowledged that philosophy and laws, and all useful arts were the inventions of the gods. Therefore, since it is manifest that men whom the Scriptures term 'carnal' are so acute and clear-sighted in the investigation of inferior things, their example should teach us how many gifts the Lord has left in possession of human nature, notwithstanding its having been despoiled of the true good....
Nor is there any ground for asking what concourse the Spirit can have with the ungodly, who are altogether alienated from God. For what is said as to the Spirit dwelling in believers only, is to be understood of the Spirit of holiness, by which we are consecrated to God as temples. Notwithstanding this, he fills, moves and invigorates all things by virtue of the Spirit, and that according to the peculiar nature which each class of beings has received by the Law of Creation. But if the Lord has been pleased to assist us by the work and ministry of the ungodly in physics, dialectics, mathematics, and other similar sciences, let us avail ourselves of it, lest, by neglecting the gifts of God spontaneously offered to us, we be justly punished for our sloth John Calvin (Institutes 2:2:15-16).
If we discard common grace, we are driven inevitably to one of two conclusions; either man is not totally depraved. He can do good of himself; or the good which he does is not really good at all. His virtues, his patriotism, marital fidelity, filial piety, love of his children, common honesty are all of them glittering sins. In the doctrine of man the denial of common grace leads to rankest Modernism or blackest misanthropy. --R B Kuiper