In the letter of dedication by René Descartes to the Dean and Doctors of the Faculty of Sacred Theology of Paris, to whom he appealed for support in promulgating the principles contained in his “Meditations on First Philosophy …”, he erroneously concluded from Romans 1:19 that by reason alone one could show the existence of God and the soul.
“And in Romans, Chapter 1, it is said that they are ‘without excuse.’ And again in the same passage it appears we are being warned with the worlds: “What is known of God is manifest in them,” that everything that can be know about God can be shown by reasons drawn exclusively from our own mind.”
Who cannot immediately see that the great Descartes has gone too far in his inference. It does not say that *everything* that can be known about God follows from ‘a prior’ principles and unaided reason, but rather that specific things about God are manifest in all men, as God has made it part of their nature i.e., ‘a priori’ (revealed law in his nature) and in the creation of the universe external to man, has provided the stimulus of discovery of “first truths of reason” in man.
The error of some Open Theists is in going too far in the other direction in denying that certainty about morals or even any attributes of God is possible or legitimately claimed. That error should be obvious in what Paul further says:
“…for God hath shewed it unto them. For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: (Rom. 1:19-20)
Those are discrete aspects of God: eternal power and divinity. Even without the Bible every person in possession of right reason has default views, given by God, of moral law and the perception of his infinite power and identity as creator of all things.