I have written a loose transcript of a Greg Bahnsen lecture entitled, Challenge to Unbelief: Self-Deception.
An argument between a believer and unbeliever is not about isolated particular facts and evidences like the resurrection of Jesus and the creation account, but rather the argument between a believer and unbeliever is about entire worldviews. The argument is between two outlooks of life that tells us about the nature of reality, how we know what we know and how we should live our lives. We have worldviews that are in collision. Because worldviews control the way we understand evidence, the way we reason and how we evaluate things, the believer and unbeliever will not be able to convince one another by appealing directly to evidence or argumentation that should lead them to agreed upon premises to a conclusion that shows the Christian is right and the non-believer is wrong. But rather, the argument will be an indirect argument.
The certainty of Christianity is seen in that God presents in his own word, authorization for his own authority. God authorizes himself. His word has that kind of self-validating power and authority with it. However, people who have hearts unwilling to believe this are not going to submit just because we claim that God says something. It is necessary then to show that unbelievers do not have a system of thought which makes sense out of science, morality, logic, human freedom etc. In traditional apologetics their ability to account for these things are taken for granted and we move onto things where we disagree like the resurrection of Jesus and miracles. However, as presuppositionalists, we instead present Christ’s underlying authority of those things which we take for granted about man and his place in the universe and about logic, morality, science etc. We challenge the foolish unbeliever to offer an alternative system of thought, which can account for human experience (logic, morality, science, human dignity etc.) We argue from the impossibility of the contrary. Christianity is true because without it you cannot prove anything!
An unbeliever should be completely without knowledge because their worldview undermines all rationality:
“For 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, and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things.
Therefore God gave them up in their lusts of their hearts to impurity, to the dishonoring of their bodies among themselves, because they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever! Amen.”
(ESV, Romans 1:18-25)
Unbelievers understanding of the world, life, knowledge and values makes nonsense out of things which we take for granted. Their understanding makes it impossible that there be moral absolutes, laws of logic, science etc. If nonbelievers lived consistently with their philosophy of life they profess, they would know nothing. But they do know things. How is this possible? Unbelievers say one thing, but believe another. The unbeliever says He doesn’t believe in a personal and absolute God, but the Bible says he does believe in such a God. The unbeliever says one thing, but believes another. When a person lies, they say one thing with their mouths, but believe something else in their heart or mind. Why do they do this? When that non-believer can’t believe something that is too difficult to believe, they start “rationalizing” or distorting the weight of evidence. This is called self-deception. It is lying to yourself about something that is too painful to believe.
Philosophers will say that self-deception is impossible to happen because when I lie to somebody else I must believe something (premise or claim) to be false and yet get somebody else to believe that it is true. So the one doing the deceiving knows that claim to be false and the person who is being deceived believes that it’s true. These are contrary to one another. However, when we lie to ourselves them we are both the ones who believe a claim to be true and the one who believes it to be false. How could this possibly happen? How can someone believe something to be true and false at the same time?
The Bible though describes this condition in Romans 1:18-25. The unbeliever knows God as a judge who is angry with them for their sins. They know that they stand guilty before God. Paul states that unbelievers “suppress the truth”. Unbeliever want to distort the weight of evidence of God’s invisible attributes that “have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse.” The unbeliever consciously and deliberately chooses not to look at the evidence clearly. He chooses not to deal with his sins before God. He chooses to rationalize the evidence so that he could be more comfortable with living his life and the idea about God. The unbeliever will try to live consistently with his beliefs about himself. He’s going to try to persuade himself with his atheistic life style that he genuinely doesn’t believe God does not exist.
What hope is there for the self-deceivers? We must show them that the unbeliever is lost spiritually and intellectually. We must argue that without the truth of God argued in the Bible they could not know anything. There is no way to knowledge except through Jesus Christ! Ultimately though it does not matter how intellectual and good at debating we are. We can’t change someone’s heart, only the Holy Spirit can. Ultimately it is the Holy Spirit who can grant them the gifts of repentance and faith!