Deceitful and Desperately Wicked (William S. Plumer, 1802-1880)

Jeremiah 17:9

“The heart is deceitful above all things, and desperately wicked: who can know it?” 

Man is the only creature on earth that seems to practice self-deception. That we should sometimes deceive others is proof of our depravity; but that we should spend our lives in self-deception is truly astonishing. Men of the fewest virtues commonly have the highest thoughts of
themselves. How strange and yet how common that he, whose heart has deceived him a thousand times, should yet confide in it as if it had always been honest! 

The human heart deceives every being but one. It would deceive Him, if He were not omniscient. None but God knows all the depths of iniquity and duplicity within us. 

Though the language of the Bible is strong, it is just. God declares, and every Christian knows by sad experience—that his heart is deceitful above all things. A perfect knowledge of the treachery of our hearts is possessed by none but God.

The heart is also VILE. It is "desperately wicked." It loves vanity, and folly, and sin. It hates holiness, and truth, and divine restraints. It is a sink of iniquity, a pool of pestilential waters, a cage of unclean birds, a sepulcher full of dead men's bones. It is torn by wild, fierce, unhallowed passions. It rejects good and chooses evil. It is wholly corrupt. It is full of evil.There is no soundness in it.

" For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies:" Matthew 15:19

"He that trusteth in his own heart is a fool: but whoso walketh wisely, he shall be delivered." Proverbs 28:26