Jesus answers this question for us: “For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander” (Matthew 15:19). And then: “What comes out of a man is what makes him ‘unclean.’ For from within, out of men’s hearts, come evil thoughts, sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly. All these evils come from inside and make a man ‘unclean’ ” (Mark 7:20–23).
In these passages, Jesus reveals the very springboard of our wants: our fleshly desires come from our innermost being. Sin does not just come about as a result of outside forces. It is borne from those hidden little niches residing in our thoughts and intentions, from the secret desires which only the mind and heart can envision. The bottom line is that, in our fallen state, the desires of our hearts do not come from God. Jeremiah further confirms the nature of man’s heart: “The heart is deceitful above all things and beyond cure. Who can understand it?” (Jeremiah 17:9)
It has long been the view of many that all humans are basically good and decent and that it is the circumstances of life such as poverty or poor nurturing that turn us into murderers and thieves. But the Bible teaches that all men suffer from a common frailty—sin. The apostle Paul calls it our sin nature. “I know that nothing good lives in me, that is, in my sinful nature. For I have the desire to do what is good, but I cannot carry it out. For what I do is not the good I want to do; no, the evil I do not want to do—this I keep on doing. Now if I do what I do not want to do, it is no longer I who do it, but it is sin living in me that does it” (Romans 7:18–20). Our evil hearts lead us to sin.
Furthermore, the heart is so corrupt and deceitful that our motives are unclear even to ourselves. As sinful creatures we devise and create evil things in the arrogance and self-sufficiency of our hearts (Proverbs 16:30; Psalm 35:20; Micah 2:1; Romans 1:30). The truth is that only God can examine our deepest motives and inward desires and only by His power can we ever hope to untangle the uncertainty and depravity that is bound up within our hearts. He alone searches all and knows us intimately (Hebrews 4:11–13).
Fortunately, God does not abandon us in our struggles with hurtful desires and sinful tendencies. Instead, He provides us the grace and strength we need to resist and overcome sin when it crouches at the door of our hearts. The psalmist tells us to: “Delight yourself in the LORD and He will give you the desires of your heart. Commit your way to the LORD; trust in Him and He will do this: He will make your righteousness shine like the dawn, the justice of your cause like the noonday sun” (Psalm 37:4–6).
Here we see that God can literally plant His own desires into the heart of man, the heart that, without Him, is desperately wicked and deceitful. He replaces the evil with good and sets our hearts on the path toward Him, removing our own desires and replacing them with His. This only happens when we come to Him in repentance and accept the gift of salvation through the Lord Jesus Christ. At that point, He removes our hearts of stone and replaces them with hearts of flesh (Ezekiel 11:19). He accomplishes this by the supernatural implanting of His Spirit into our hearts. Then our desires become His desires, our wills seek to do His will, and our rebellion turns to joyous obedience.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.