What does it mean that the heart is desperately wicked in Jeremiah 17:9?

But then it may be said; and is said by many, that while some very terrible samples of fallen humanity are capable of committing some of the abominable sins prohibited in scripture, yet all are not so. This is a most thorough mistake. Hear what the Holy Ghost says, in the seventeenth chapter of the prophet Jeremiah. "The heart is deceitful above all things, and desperately wicked." Whose heart is he speaking of? Is it the heart of some atrocious criminal, or of some untutored savage? Nay; it is the human heart, the heart of the writer and of the reader of these lines.

The heart of man is incurable, however, and so deceitful is it that no one of Adam’s sinful stock can fathom its depravity (v. 9). It is set to do evil and to depart from God, however greatly privileged it may be. The Lord was testing man in the Old Testament, testing favoured Israel under law, but only to prove his utter ruin (v. 10). Judgment must therefore fall. For believers now it has already taken place at the cross of our Lord Jesus Christ; governmentally it fell upon the nation as the prophet foretold, and even the covetous King Jehoiakim becomes an individual example. From his ill-gotten goods he was cut off in the midst of his years (at 36), like a partridge might be taken from her many eggs. As Nabal, at his end, he was a fool (v. 11); so is every man who follows the subjective promptings of his own heart and forsakes the Lord.

"The heart is deceitful above all things, and desperately wicked: who can know it? I the Lord search the heart, I try the reins, even to give every man according to his ways, and according to the fruit of his doings" (Jer. 17:9). The doctrine of the desperate wickedness of the heart, as a truth of universal application, is the verdict of divine Omniscience, however questioned by individual experience. Every believer in the Lord Jesus Christ has doubted it in his own case, till he has been taught it by God Himself. But after this lesson so taught of God, and acquiring depth by increasing experience, it is another lesson to learn practically the deceitfulness of the heart. The reception of this doctrine in the power of it, helps to keep the believer humble and watchful. Thus, "the Lord keepeth the feet of His saints," putting His fear in their hearts. And being in the fear of the Lord all the day, they are kept from many an outbreak of desperate wickedness, the common result of walking in self-confidence. "For he that trusteth in his own heart is a fool."

If I examine my own heart I cannot find it out. I know more of God's heart than I do of my own; for my own is so subtle I cannot get to the bottom of it; for "the heart is deceitful above all things, and desperately wicked: who can know it?" and the best man upon earth will be the first to confess this.

Verses 5-11. A curse is pronounced upon him who trusteth in man, who departeth from the Lord. For such a one there is no hope; he shall not see good; he must be an outcast, like the heath in the desert. And such is the natural condition of man, his heart is departed from the Lord, he trusteth in himself, making flesh his arm to defend and to uphold. But blessing is for the man who trusteth in the Lord, whose hope the Lord is. Verse 8 contains the same truth as Psalm 1:3. It is a description of the God-fearing in Israel, who knew the Lord, trusted and hoped in Him. He had called them to this place of blessing; He had encouraged them to trust in Him; He had manifested His glory and His power in their midst. But they turned away from Him, they leaned not on Him, but on the arm of flesh, on Egypt. The heart is the source of it, deceitful above all things and desperately wicked. The question, "Who can know it?" is answered, "I the LORD search the heart." He has sounded the depths of it and in His omniscience knew the shameful history of Israel, and all their backsliding. So He knew and knows what we are, yet in sovereign love and grace He has loved us and bears with His own.

He did not think himself a dog. He was ready to resent the imputation. The thought of such deeds might have been abhorrent alike to his judgment and feelings. He was not aware of the deceitfulness of the heart. The prophet does not accuse Hazael of perfidy or of hypocrisy, but simply replies: "The Lord hath showed me that thou shalt be king over Syria." Hazael was ignorant both of the deceitfulness and desperate wickedness of the heart. He knew not how many checks there are in the things around us, and from the position in which we are, to hinder the outbreak of the desperate wickedness of the heart, which is unsuspected; because it lies, as it were, dormant, till aroused by circumstances. Hazael, as a prime minister, had tasted power, but the sickness of his master now presented the opportunity of passing from the responsible power of a minister to the irresponsible power of a usurper; and did he know or suspect the way to crime thus opened before him? Does the slave, groaning under the yoke of the oppressor, suspect that oppression is in his own heart; and, if he changed places with his oppressor, it would break forth into action. … The heart is so deceitful as to hide from itself what is in it, so as to be taken by surprise at the outbreak of evil.

Hazael protests that he is not a dog that he should act with such callous brutality. Probably his protest is entirely sincere. Such deeds might have been foreign to his thoughts, and even abhorrent to his feeling at the moment. He did not know his own heart. He was not aware that the heart is deceitful above all things, and desperately wicked. As with ourselves, too often, he little realized the depth of wickedness and cruelty in the heart that is held in check by many a safeguard until, suddenly aroused by circumstances which give the occasion, it blazes forth in all its horror. Instead of asking, "Is thy servant a dog?" far better would it have been for Hazael, as for ourselves, to take the ground of the Syrophenician woman who owned that she was indeed a dog, only to discover that there is grace in the heart of God even for a dog (Mark 7:24-30).

The testimony of Scripture on this great question, is distinct and conclusive, "There is no difference." Men do not like this. It is too levelling for them. Self-righteousness is cut out by the roots by this sweeping statement of inspiration. Man likes to establish distinctions. He cannot bear to be placed in the same category with the Magdalenes and the Samaritans, and such like. But it cannot be otherwise. Grace levels all distinctions now; and judgement will level them all by-and-by. If we are saved, it is in company with Magdalenes and Samaritans; and if we are lost, it will be in company with such likewise. There will, no doubt, be degrees of glory; as there will be degrees of punishment; but as to the real nature and character of the human heart, "there is no difference." "The heart is deceitful above all things, and desperately wicked." What heart? Man's heart — the heart of the writer and the reader of these lines. "For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies." Out of what heart? Man's heart — the heart of the writer and the reader of these lines. These things could not come out of the heart if they were not there; and if they do not come out in action, it is not because they are not there, but that circumstances have operated to prevent.

The four thousand years of man’s probation have proved him to be unmendably evil, the thoughts and imaginations of his heart only evil continually, and the more favourable his circumstances the more rebellious and unclean his ways. His activities are always reprobate, for they proceed from his own evil heart, and “the heart is deceitful above all things, and desperately wicked: who can know it?” “I the Lord search the heart,” and therefore He alone can tell us what it is (Jer. 17:9). We are dependent upon Him to tell us what we are, and He does it, in order that we may turn to Him, as those that are afraid of themselves, and find in Him One who is able to deliver us from that which we by nature are.

"And Peter answering to Him said, Expound to us this parable. But He said, Are ye also without intelligence? Do ye not apprehend that everything that enters into the mouth finds its way into the belly, and is cast forth into the draught? but the things which go forth out of the mouth come out of the heart and these defile men. For out of the heart come forth evil thoughts, murders, adulteries, fornications, thefts, false witnessings, blasphemies; these are the things which defile man, but the eating with unwashed hands does not defile man" (v. 15-20). How slow they were to understand the full meaning of what He wanted to convey to their hearts. Our Lord shows the true source of all defilement. It is within. The Pharisees did not believe in the utter corruption of the heart. "I the Lord search the heart" (Jer. 17:10). And this searcher of hearts is present here on the scene and throws His own light upon the source of evil, of which He had said through Jeremiah, "The heart is deceitful above all things, and desperately wicked." Blessed is he who bows before this verdict.