Paul says something that people, even professing Christians, don’t like: “The wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. For what can be known about God is plain to them, because God has shown it to them. 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. For although they knew God, they did not honor Him as God or give thanks to Him, but they became futile in their thinking, and their foolish hearts were darkened. Claiming to be wise, they became fools” (Romans 1:18-22). His point here is that all men know God and our accountability to Him, because he has revealed Himself in His works, so that no man can claim ignorance as an excuse for unbelief. Unbelief is the result of a choice, not of innocent ignorance.
Paul applies that principle to his evangelistic sermon at the Areopagus in Athens (Acts 17:16-34) at about the same time that he was writing Romans. “So Paul, standing in the midst of the Areopagus, said: ‘Men of Athens, I perceive that in every way you are very religious. 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. The God who made the world and everything in it, being Lord of heaven and earth, does not live in temples made by man,nor is He served by human hands, as though He needed anything, since He himself gives to all mankind life and breath and everything. And He made from one man every nation of mankind to live on all the face of the earth, having determined allotted periods and the boundaries of their dwelling place, that they should seek God, and perhaps feel their way toward Him and find him. Yet He is actually not far from each one of us, for ‘In Him we live and move and have our being’;as even some of your own poets have said, ‘For we are indeed his offspring’” (Acts 17:22-28). Paul uses the altar to the “unknown god” to prove that the Athenians know about, but do not know savingly, the one true God. Therefore, he has come to reveal to them the God that they have known about, so that they may now repent of the deliberate ignorance (verse 30), and come to know the God who had been unknown before. Even the pagan poetry which he quotes, Paul uses as evidence that there is a breaking out of the underlying knowledge of the true God, though that knowledge had been suppressed in the confusion of the Greek mythological religion.
Contrary to traditional apologetics, biblical apologetics does not try to prove the existence of a god. The unbeliever already believes that. Therefore, the presuppositional apologist directs his apologetic to what the unbeliever already knows, but wants to avoid, with the goal being the unbeliever’s repentance.