John MacArthur: Watch over Your Heart

by John MacArthur (

A good cleaning, a fresh paint job, and some gardening can make a great difference to the outward appearance of your home. But if the house is rotting from the inside—if it’s infested with vermin and filled with garbage and filth—all that work on the exterior is wasted effort.

The same principles hold true for your spiritual life. It is relatively easy to confess and forsake deeds of sin, sins of omission, and unintentional sin. But the sins of our thought life are soul‑coloring sins, character‑damaging sins. Because they work so directly against the conscience and will, dealing with them honestly and thoroughly is one of the most difficult aspects of mortifying our sin. If we ever want to see real progress in sanctification, however, this is an area where we must attack and destroy our sinful habits with a vengeance.

The Old Testament sage wrote, “Watch over your heart with all diligence, for from it flow the springs of life” (Proverbs 4:23).

God knows our hearts (Acts 15:8). David wrote, “You understand my thought from afar . . . and are intimately acquainted with all my ways. Even before there is a word on my tongue, behold, O Lord, You know it all” (Psalm 139:2-4). Why, then, would we ever feel free to indulge in gross sins in our imagination—sins we would never act out before others—when we know that God is the audience to our thoughts? “Would not God find this out? For He knows the secrets of the heart” (Psalm 44:21).

Jesus told the Pharisees, “You are those who justify yourselves in the sight of men, but God knows your hearts; for that which is highly esteemed among men is detestable in the sight of God” (Luke 16:15). Is not what we do in the sight of God infinitely more important than what we do in the sight of others?

Moreover, the thoughts of our heart are the real litmus test of our character: “As he thinks within himself, so he is” (Proverbs 23:7). “A worthless person, a wicked man, is the one . . . who with perversity in his heart continually devises evil” (Proverbs 6:12-14). Do you want to know who you really are? Take a hard look at your thought life. For “as in water face reflects face, so the heart of man reflects man” (Proverbs 27:19). External behavior is not an accurate gauge of your character; the thoughts of your heart reveal the truth. Only your conscience and God can assess the real truth about you.

Job’s “comforters” falsely accused him of an impure thought life. Zophar was sure he understood Job’s real problem: “Evil is sweet in his mouth, and he hides it under his tongue, though he desires it and will not let it go, but holds it in his mouth” (Job 20:12-13). The picture he painted of the evil thinker is vividly true‑to‑life. Evil thoughts are like candy to them. They derive great satisfaction from their imaginary sins. They savor their evil fantasies. They relish them like a choice morsel of sweetness under the tongue. They roll them around in their imagination. They return to the same wicked musings from which they can glean illicit pleasure over and over again. They mull them over like an animal chewing the cud, bringing up their favorite evil thoughts time and time again to reenact them anew in the mind.

But Zophar misjudged Job. Job had carefully guarded himself against wicked and lustful thoughts: “I have made a covenant with my eyes; how then could I gaze at a virgin?” (Job 31:1). He knew God was audience to his thoughts. “Does He not see my ways, and number all my steps? If I have walked with falsehood, and my foot has hastened after deceit, let Him weigh me with accurate scales, and let God know my integrity” (Job 31:4-6). Job denied that his heart had followed his eyes (Job 31:7). He denied that his heart had been enticed by another woman (Job 31:9). “That would be a lustful crime . . . an iniquity punishable by judges,” he acknowledged (Job 31:11). To hide iniquity in the bosom, he said, would be to cover one’s transgression like Adam (Job 31:33). The very thought appalled his righteous mind.

Clearly, Job was well aware of the danger of sinful thoughts. He had consciously, deliberately set a guard in his heart to avoid any such sin. He even offered special sacrifices to God just in case his children sinned in their hearts: “When the days of feasting had completed their cycle, Job would send and consecrate them, rising up early in the morning and offering burnt offerings according to the number of them all; for Job said, ‘Perhaps my sons have sinned and cursed God in their hearts.’ Thus Job did continually” (Job 1:5, emphasis added). Job’s careful safeguarding of his thought life seems to have been the very reason God singled him out for unique blessing. “There is no one like him on the earth,” the Lord told Satan. “[He is] a blameless and upright man, fearing God and turning away from evil” (Job 1:8).

Job understood what the Pharisees stubbornly refused to see: that just because you don’t act out an evil deed, that doesn’t excuse the secret desire. Lust itself is sinful. Greed alone is wicked. Covetousness, anger, pride, concupiscence, envy, discontent, hatred, and all evil thoughts are just as bad as the behavior they produce. To treasure such thoughts in the heart and relish the thought of them is an especially grievous sin against God, because it adds hypocrisy to the original evil thought.

This article originally appeared here at Grace to You
Copyright 2012, Grace to You. All rights reserved.  Used by permission

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