The problem with these suggestions is Jesus’ own teaching. In Mark 7, He makes a point of highlighting what defiles a person. Much like the fascination many today have with “self-care” through eating the right foods and engaging in healthy practices, the Pharisees and scribes of Jesus’ day established traditions such as the proper washing of hands, pots, and even couches. However, for many Pharisees, these went beyond “self-care” to having a role in securing one’s righteousness before God (vv. 1–13). This approach presumes that the basic human problem comes from the outside. Jesus teaches the exact opposite:
“Hear me, all of you, and understand: There is nothing outside a person that by going into him can defile him, but the things that come out of a person are what defile him.” And when [Jesus] had entered the house and left the people, his disciples asked him about the parable. And he said to them, “Then are you also without understanding? Do you not see that whatever goes into a person from outside cannot defile him, since it enters not his heart but his stomach, and is expelled?” (Thus he declared all foods clean.) And he said, “What comes out of a person is what defiles him. For from within, out of the heart of man, come evil thoughts, sexual immorality, theft, murder, adultery, coveting, wickedness, deceit, sensuality, envy, slander, pride, foolishness. All these evil things come from within, and they defile a person.” (Mark 7:14–23)
In teaching against a twisted understanding of humanity, Jesus makes precisely Jeremiah’s point: the human heart is the enduring problem. The human heart is what makes men and women wicked and causes them to do wicked things. Thus, if there is going to be any lasting spiritual remedy for humanity, it must address the root problem—our desperately wicked hearts. And that is exactly what Scripture teaches: true religion starts in the heart.
King David is the great biblical figure of the heart. He is commended to the people of God because he was a man after God’s “own heart” (1 Sam. 13:14). And he pursued God because his own heart had been touched by God’s grace. Perhaps the greatest testimony to this is what David did when convicted of sin. After finally seeing his sins against Bathsheba and Uriah for what they were, he petitioned God in Psalm 51 for a clean heart.
A heart apart from God’s grace is desperately wicked but doesn’t know it. A heart touched by God’s grace might still slip into wickedness, yes, but it will knowingly turn in repentance and faith in God and find cleansing in His grace.
If David’s prayer of repentance reminds us that the cleansing of our hearts comes through a source outside us, the writer to the Hebrews points us to the specific source of that cleansing: “Let us draw near with a true heart in full assurance of faith, with our hearts sprinkled clean” by the blood of Christ (Heb. 10:22–23). The cleansing of our desperately wicked hearts comes through an application of the blood of Christ shed once and for all on the cross. Once cleansed, though, where does a Christian heart go?
The Christian’s heart, is strengthened through the Word of God. Later in Hebrews, when the writer is encouraging good teaching and warning against strange teaching, he says, “It is good for the heart to be strengthened by grace” (13:9). He makes clear the content of that grace is Jesus Christ, who “is the same yesterday and today and forever” (v. 8).
Scripture never says a cleansed heart cannot sin. Just look at David. But unlike a wicked heart that doesn’t know its own sickness, the heart cleansed by the blood of Christ knows it needs to—and wants to—grow in the grace of Christ. The Christian knows there are no inherent resources for this growth but only comes as we receive good teaching from the Word of God and the Spirit writes that very Word on our hearts (Heb. 8:10).