“Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled” (Titus 1:15).
Nothing corrupts the conscience more deeply than the unchecked habit of entertaining sinful thoughts. Once such a habit begins, it takes root quickly, embedding itself into one’s mindset. This makes it easier to yield to temptation. The mind needs no occasion to sin. It can conjure up evil in any moment, in any setting, under any condition.
Be Aware of Danger of Sinful Thought-Life
Evil thoughts are the seedbed of all sin. Jesus warned, “But those things which proceed out of the mouth come forth from the heart; and they defile the man. For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies” (Matthew 15:18-19).
As the saying goes, “Sow a thought, reap an act. Sow an act, reap a habit. Sow a habit, reap a character. Sow a character, reap a destiny.” If we allow our minds to indulge in wicked thoughts and sinful fantasies, we stir up passions and desires that could drive us to sin.
Inner corruption is as grievous as outward acts of sin. So, Jesus taught us to examine our hearts and nurture inward purity. A man may not physically kill, but he is guilty of murder when he harbours hatred. Jesus said, “But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment … whosoever shall say, Thou fool, shall be in danger of hell fire” (Matthew 5:22)! Similarly, one may not commit adultery outwardly, but Jesus said, “That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart” (Matthew 5:28).
Instructively, although the Pharisees and religious leaders of Jesus’ time considered themselves righteous, Jesus exposed them as thoroughly corrupt because of the evil intentions and thoughts that ruled their hearts. He declared, “Woe unto you, scribes and Pharisees, hypocrites! for ye are like unto whited sepulchres, which indeed appear beautiful outward, but are within full of dead men’s bones, and of all uncleanness. Even so ye also outwardly appear righteous unto men, but within ye are full of hypocrisy and iniquity” (Matthew 23:27-28). Hence, Scripture declares, “For as he thinketh in his heart, so is he” (Proverbs 23:7a).
Beware of Sinful Activities of the Mind
Should we not be vigilant about what we allow into our minds? Scripture warns that “A heart that deviseth wicked imaginations” (Proverbs 6:18a) is detestable to God. We must, therefore, be alert to the following sinful tendencies of the mind:
The Sin of “Remembering”
One way the mind sins is by delighting in memories of past sins. Ezekiel 23:19 describes Israel’s downfall: “Yet she multiplied her whoredoms, in calling to remembrance the days of her youth, wherein she had played the harlot in the land of Egypt.” Israel repeatedly recalled past indulgences, eventually returning to them.
Is this not true for many believers today? Satan digs up past filth and seeks to revive it in our minds. Once implanted, such images are difficult to erase. They linger, tempting us afresh. This is why pornography and much of modern entertainment are so spiritually harmful—they store corrupting content in the memory, ready to lure us again.
The Sin of “Scheming”
The second way the mind sins is by plotting future evils. Psalm 36:4 says, “He deviseth mischief upon his bed; he setteth himself in a way that is not good; he abhorreth not evil.” The wicked man lies in bed, crafting sinful plans, exposing himself to grave moral danger.
When such scheming minds unite, they “encourage themselves in an evil matter: they commune of laying snares privily” (Psalm 64:5). They “search out iniquities… both the inward thought of every one of them, and the heart, is deep” (Psalm 64:6). God condemns such plotting hearts, because “Deceit is in the heart of them that imagine evil” (Proverbs 12:20a). Isaiah 32:6-7 also warns of those who devise wicked schemes to harm others, even the vulnerable. “For the vile person will speak villany, and his heart will work iniquity, to practise hypocrisy, and to utter error against the LORD, to make empty the soul of the hungry, and he will cause the drink of the thirsty to fail. The instruments also of the churl are evil: he deviseth wicked devices to destroy the poor with lying words, even when the needy speaketh right.” God abhors this form of mental sin.
The Sin of “Imagining”
Thirdly, the mind can sin through fantasy. People imagine indulging in lust, exacting revenge, or carrying out evil acts. Whether fantasising about illicit affairs, robbery, or violence, such mental exercises are destructive.
Are these sins real? Absolutely. They defile the soul and often lead to real-life sin. James 1:15 teaches, “Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.” Let us not forget the reason for the global flood judgment in Noah’s day: “GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually” (Genesis 6:5).
(This article has been adapted and revised from a pastoral article originally published in Bible Witness, Vol. 22, Issue 4.)