John Piper says something provocative in a sermon about the woman at the well:
Now watch the universal reflex of a person trying to avoid conviction. She has to admit in verse 19 that Jesus has extraordinary insight (“You’re a prophet!”), but instead of dealing with her guilt, she tries to suck Jesus into an academic controversy.... A trapped animal will chew his own leg off. A trapped sinner will mangle his own mind and rip up the rules of logic and discourse.... [T]hat kind of double-talk and evasive, verbal footwork is very common. And texts like this incline me to think that wherever I hear it, someone is hiding something. If your conscience is clean, reason can hold sway; if it’s not, you will be instinctively irrational.
I came across this idea before in a book by James Spiegel, and from what I’ve observed, I think it’s true—a real danger we all need to guard against.
[A]nother way that virtuous living helps cognition and, in turn, theistic belief is by preventing motives for willful disbelief. A vicious or immoral person has a motive to reject vital truths that condemn his or her lifestyle. So the less vice in one’s life, the fewer ulterior motives one will have to disbelieve such truths, whether they concern ethics or the reality of God. Put another way, one’s sinful commitments cause cognitive interference by the will, so the more virtuous person will be less susceptible to such interference. All of these considerations confirm E. Michael Jones’s insight [in Degenerate Moderns: Modernity as Rationalized Sexual Misbehavior] that “the intellectual life is a function of the moral life of the thinker. In order to apprehend truth, which is the goal of the intellectual life, one must live a moral life.”
I’ve seen Christians fall into sinful patterns and, as a result, begin to distort their biblical interpretations in an unconscious attempt to wrap their theology around their sin. They’ve harmed their very ability to reason.
It terrifies me.
This is another reason for us to flee at the first sign of temptation. Protect your ability to reason and see God clearly! As apologists, this is absolutely crucial. Spiegel makes some suggestions:
The study of Scripture and singing of hymns directly impact our cognitive processes, of course. But fasting, sacrifice, and other practices of self-denial build self-control, which enables a person to better resist all sorts of temptations. This translates into a reduction of sin in one’s life, and for the reasons just explained, this will bring cognitive benefits, including insights into theological truth.
We can think clearly when we’re not in sin because we have nothing to fear. We don’t need to protect ourselves from the truth if we have nothing to hide or explain away; and the good news is, because of the Gospel, even when we do sin, we need not either hide it or explain it away. The fact that “there is now no condemnation for those who are in Christ Jesus” removes all fear and need to hide. God’s grace provides the space for us to humble ourselves and be open about our sin before God and others. That is freedom! Live in that freedom by fighting your sin and confessing it before God when necessary, and you will protect your rationality.