In 1.3.1 Francis Turretin, while discussing the subject of theology in general, answers the question “Whether natural theology may be granted?”
The question focuses on natural theology after the Fall not on the theology of Adam prior. Turretin asks if there is a natural faculty implanted in humanity that embraces the capability of understanding and the natural first principles of knowledge (which the Reformed maintain). He isn’t asking if this knowledge of God, which all humanity has, is perfect for saving, for we affirm that after the Fall, it was insufficient for salvation. Rather it is maintained that any knowledge of God, which remains in man, is sufficient to lead humanity to conclude that God exists and demands worship.
There was a group during the Reformation called the Socinians who denied any sort of natural theology or knowledge of God. This idea is still prevalent today. Some are convinced that humanity for the most part isn’t aware that God exists. Adamant skeptics will even claim that they are searching for the truth about the existence of God or any divine being. In orthodox teaching, we affirm there is a natural theology or natural knowledge of God. By this term we mean that there is knowledge of God that is “partly innate” and “partly acquired”.
Turretin is helpful here as he cites Romans 2 for Scriptural proof of the natural knowledge of God that all of humanity possesses.
Romans 2:14 For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law. 15 They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them
The natural law is written on our conscience. It is the conscience that accuses and guides all in their moral actions. We know the law of God naturally by our “instinct”. It is by implication we can conclude, since humanity has knowledge of God’s law they also have knowledge of God.
Romans 2:14-15 testifies that our conscience makes us aware that God distinguishes good from evil and is just in his judgments. This is demonstrated from the text, since when the Apostle writes a “work of the law” he means that we can distinguish between good and evil, and we are moved to do one and avoid the other. This law is “written” and this writing of the law implies a natural revelation of that law to the conscience. The natural revelation is opposed to the external revelation given to the Jews on Sinai.
Turretin cites from other places in Scripture that serve as proof that God has given man both an innate and acquired knowledge of himself:
Psa. 19:1 The heavens declare the glory of God, and the sky above proclaims his handiwork.
Acts 14:15 “Men, why are you doing these things? We also are men, of like nature with you, and we bring you good news, that you should turn from these vain things to a living God, who made the heaven and the earth and the sea and all that is in them. 16 In past generations he allowed all the nations to walk in their own ways. 17 Yet he did not leave himself without witness, for he did good by giving you rains from heaven and fruitful seasons, satisfying your hearts with food and gladness.”
Acts 17:23 For as I passed along and observed the objects of your worship, I found also an altar with this inscription, ‘To the unknown god.’ What therefore you worship as unknown, this I proclaim to you.
Rom. 1:19 For what can be known about God is plain to them, because God has shown it to them. 20 For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse.
The knowledge of God is natural in humanity. Yet there will still be those who deny the existence of God and they do so out of ignorance and determination to hold to their rebellion. Those who reject God and the Gospel are not ignorant they are in rebellion. They are in search of truth but in the denial of it.