Jeremiah 17:9

The heart is deceitful above all things
This is the source of the idolatry and creature confidence of the Jews, sins which were the cause of their ruin; and though what is here said is particularly applicable to their hearts, yet is in general true of the heart of every man; which is "deceitful", and deceiving; and puts a cheat upon the man himself whose it is: it deceives him with respect to sin; it proposes it to him under the notion of pleasure; it promises him a great deal in it, but does not yield a real pleasure to him; it is all fancy and imagination; a mere illusion and a dream; and what it gives is very short lived; it is but for a season, and ends in bitterness and death: or it proposes it under the notion of profit; it promises him riches, by such and such sinful ways it suggests; but, when he has got them, he is the loser by them; these deceitful riches choke the word, cause him to err from the faith, pierce him through with many sorrows, and endanger the loss of his soul: it promises honour and preferment in the world, but promotes him to shame; it promises him liberty, but brings him into bondage; it promises him impunity, peace, and security, when sudden destruction comes: it deceives him in point of knowledge; it persuades him that he is a very knowing person, when he is blind and ignorant, and knows nothing as he ought to know; and only deceives himself; for there is no true knowledge but of God in Christ, and of a crucified Christ, and salvation by him; see ( 1 Corinthians 3:18 ) ( 1 Corinthians 8:1 1 Corinthians 8:2 ) ( Galatians 6:3 ) it deceives in the business of religion; it makes a man believe that he is a very holy and righteous man, and in a fair way for heaven, when he is far from that, and the character it gives him; in order to this, it suggests to him that concupiscence or lust, or the inward workings of the mind, are not sin; and it is only on this principle that it can be accounted for, that Saul, before conversion, or any other man, should be led into such a mistake, as to conclude that, touching the righteousness of the law, he was blameless: it represents other sins as mere peccadillos, as little sins, and not to be regarded; and even puts the name of virtue on vices; profuseness and prodigality it calls liberality, and doing public good; and covetousness has the name of frugality and good economy: it directs men to compare themselves and their outward conduct with others, that are very profane and dissolute; and from thence to form a good character of themselves, as better than others; and as it buoys up with the purity of human nature, so with the power of man's freewill to do that which is good, and particularly to repent at pleasure; and it puts the profane sinner upon trusting to the absolute mercy of God, and hides from him his justice and holiness; and it puts others upon depending upon the outward acts of religion, or upon speculative notions, to the neglect of real godliness; see ( James 1:22 James 1:26 ) . The man of a deceitful heart, the hypocrite, tries to deceive God himself, but he cannot; he oftentimes deceives men, and always himself; so do the profane sinner, the self-righteous man, and the false teacher; who attempts to deceive the very elect, but cannot; yea, a good man may be deceived by his own heart, of which Peter is a sad instance, ( Matthew 26:33 Matthew 26:35 Matthew 26:70 Matthew 26:72 Matthew 26:74 ) . The heart is deceitful to a very great degree, it is superlatively so; "above all", above all creatures; the serpent and the fox are noted for their subtlety, and wicked men are compared to them for it; but these comparisons fall short of expressing the wicked subtlety and deceit in men's hearts; yea, it is more deceitful to a man than the devil, the great deceiver himself; because it is nearer to a man, and can come at him, and work upon him, when Satan cannot: or "about", or "concerning all things" ^F17; it is so in everything in which it is concerned, natural, civil, or religious, and especially the latter. The Septuagint version renders it "deep"; it is an abyss, a bottomless one; there is no fathoming of it; the depths of sin are in it; see ( Psalms 64:6 ) and, seeing it is so deceitful, it should not be trusted in; a man should neither trust in his own heart, nor in another's, ( Proverbs 28:26 ) ( 25:19 ) , "and desperately wicked": everything in it is wicked; the thoughts of it are evil; the imaginations of the thoughts are so; even every imagination, and that only, and always, ( Genesis 6:5 ) the affections are inordinate; the mind and conscience are defiled; the understanding darkened, so dark as to call evil good, and good evil; and the will obstinate and perverse: all manner of sin and wickedness is in it; it is the cage of every unclean bird, and the hold of every foul spirit; all sin is forged and framed in it; and all manner of evil comes out of it, ( Revelation 18:1 ) ( Matthew 15:19 ) yea, it is wickedness itself, ( Psalms 5:9 ) , it is so even to desperation; it is "incurably wicked" ^F18, as it may be rendered; it is so without the grace of God, and blood of Christ:

who can know it?
angels do not, Satan cannot; only the spirit of a man can know the things of a man within him; though the natural man does not know the plague of his own heart; the Pharisee and perfectionist do not, or they would not say they were without sin; such rant arises from the ignorance of their own hearts; only a spiritual man knows his own heart, the plague of it, the deceitfulness and wickedness in it; and he does not know it all; God only knows it fully, as is expressed in the next words, which are an answer to the question; see ( 1 Corinthians 2:11 ) ( 1 Kings 8:38 ) ( Psalms 19:12 ) .