"The heart is deceitful above all things, and desperately wicked: who can know it?" -- Jeremiah 17:9
If we would understand what kind of person a man or woman is, we must understand what that person is at heart. This is what God says about the hearts of all human beings by nature: "Every imagination of the thoughts of his heart (is) only evil continually" (Gen. 6:5). His prophet Jeremiah declares, "The heart is deceitful above all things, and desperately wicked: who can know it?"
Deceitful Above All Things
The heart of man is deceitful above all things. Our hearts are so deceitful that none of us knows his own heart, before conversion or afterwards. So deceitful is the heart of man that nothing in it can be trusted. "He that trusteth in his own heart is a fool" (Pro. 28:26). Some "trust in themselves that they are righteous, and despise others." Some trust in themselves that they are "rich, and increased in goods, and have need of nothing," not knowing that they are "wretched, and miserable, and poor, and blind, and naked!" All who trust in their hearts, that they are good, are fools, for the heart is as wicked as it is deceitful.
The heart of man is desperately wicked. The heart of every person in this world, yours and mine included, is wickedness itself (Ps. 5:9). It is enmity against God (Rom. 8:7). Like Babylon, man's heart is a "cage of every unclean and hateful bird, and the hold of every foul spirit." The heart of man is the cesspool from which all sin evolves, the forge where all iniquity is formed, the slime pit from which every transgression springs (Matt. 15:19-20). The thoughts of the heart, the imaginations of the heart, the affections of the heart are all wicked. Nothing good ever arises from the heart of man. No good things comes out of this Nazareth, for there is nothing good in it. So dark is the heart of man that it has no light into spiritual things. It is darkness itself! So perverse is the heart that it calls good evil and evil good; it calls light darkness and darkness light. It is perverseness itself! The understanding of the heart is so depraved that its judgment in spiritual matters is always wrong. It is depravity itself!
The plague of the heart is so deep and secret that none can understand his errors; and there is no hope for cure but by God's sovereign grace and Christ's cleansing blood!