No sin is more destructive to the conscience than the sin that takes place in the arena of the mind. After all, who but God and the sinner ever knows about them? “Who among men knows the thoughts of a man except the spirit of the man, which is in him?” (1 Corinthians 2:11).
Many people who will not do evil deeds are nevertheless boldly evil in their thoughts. A man who abstains from fornication for fear of getting caught might convince himself it is all right to indulge in salacious fantasies because he thinks no one else will ever discover such a private sin. The sins he deliberately entertains in his mind may be a thousand times more evil than anything he would ever think of doing before others. Scripture says his guilt is the same as if he acted out his fantasies (Matthew 5:27-28).
To indulge in sins of thought, therefore, is to molest the conscience directly. Sins of the mind assault the conscience like no other sins, because the conscience is their only deterrent. Those whose thoughts are impure cannot have pure consciences; the guilt is inherent in the evil thought. When the thoughts are defiled, the conscience immediately is, too. That is why nothing is more characteristic of unbelief than an impure mind combined with a defiled conscience: “To the pure, all things are pure; but to those who are defiled and unbelieving, nothing is pure, but both their mind and their conscience are defiled” (Titus 1:15, emphasis added).
In fact, nothing damages the conscience more than the habit of indulging in evil thoughts. Unfortunately, once begun, the practice becomes all too easy. This is a sin that does not have to wait for an opportunity; the mind can sin anytime, anywhere, under any circumstances. So the habit is quickly and easily established.
By engaging the inner faculties—mind, emotions, desire, memory, and imagination—thought sins work directly on the soul to bias it toward evil. Sow a thought, reap an act. Sow an act, reap a habit. Sow a habit, reap a character. Sow a character, reap a destiny. Evil thoughts thus lay the groundwork for all other sins.
Over the next few days, we’re going to look at the real danger presented by the sins of the mind, and see how Scripture instructs us to guard our minds and our actions from the corruption of secret sin.