The heart with which all are called is deceitful above all things and desperately wicked, a condition that remains hidden even from its owner and produces subtle suggestions that call evil good while crying peace where none exists. This corrupt heart supplanting, tortuous, and full of windings continually seeks to gratify pride, ambition, evil desire, and every form of corruption, springing back into action the moment attention turns from God. Its issues flow into stubbornness, jealousy, hatred, lust, self-pity, resentment, selfishness, and every rotten attitude that justifies neglecting prayer, study, and obedience. Such a heart must be guarded with all diligence, for out of it spring the issues of life, and the only remedy lies in the Spirit and the words of Christ that alone give life while the flesh profits nothing. The same heart hardens when God's voice is not heard, producing unbelief that departs from the living God and causes one to drift from the foundation of confidence. This hardening repeats the rebellion in the wilderness, where an entire generation erred in heart, set its affection on the lust of the eyes, the lust of the flesh, and the pride of life, and therefore never entered the rest. The journey to the Kingdom requires continual choice between the old heart and the new heart God is forming. Those who hold fast the beginning of their confidence to the end, who discipline body and mind, redeem the time, walk circumspectly, and answer when Christ knocks, receive the imperishable crown rather than disqualification. The warning remains constant: never allow the heart to become hardened, lest the promised rest be missed.

The verse from Jeremiah 17:9 is often rendered to describe the heart as deceitful above all things and desperately wicked, yet research into the underlying Hebrew terms aqov and anesh indicates that these renderings are inaccurate. The heart instead contains knowledge so deep that it remains beyond full comprehension, rendering it vulnerable rather than inherently wicked. This understanding aligns with the verse's closing question concerning who can know it and receives confirmation from the Septuagint rendering, which states that the heart is deep beyond all things. Because the heart is therefore prone to deception from the surrounding world, it requires diligent guarding, as the issues of life proceed from within the inner person. God searches the heart and tests the mind in order to render to each individual according to the fruit of his or her deeds. This divine examination distinguishes those whose hearts depart from the Lord and fall under a curse from those who trust in Him and receive blessing. The same inner reality accounts for the evil that proceeds from within a person, as later illustrated when every intent of the thoughts of the heart was found to be only evil continually in the days before the flood. Preparation of the heart is therefore essential. The heart must be made steadfast through honest confession, repentance, fervent prayer, careful meditation on God's Word, and fellowship with those of like mind. When so prepared, the peace of God guards the heart and mind, enabling trust in the Lord rather than reliance on one's own understanding and directing the path away from evil.

The heart is deceitful above all things and desperately wicked, a condition that renders it incurably sick and resistant to any human effort at reform. The Hebrew term rendered deceitful conveys a swelling pride, fraudulent vanity, and intentional perversion of truth designed to induce surrender of what is valuable, while the accompanying descriptor indicates a frailty so extreme that the heart lies at the point of death and cannot be healed. God therefore likens it to stone, impervious to truth, and promises instead to replace it with a heart of flesh that yields to His way. This incurable self-centeredness prevents consistent obedience to the two great commandments. The heart cannot love God above all or neighbor as self without placing its own interests first, thereby committing idolatry and rendering impossible the formation of character suited to God's Kingdom. Its expressions appear in the nineteen qualities listed in II Timothy 3:1-5, each an intensified manifestation of the same deceitful source. These traits—self-love, covetousness, boasting, pride, blasphemy, disobedience, ingratitude, absence of natural affection, implacability, slander, lack of self-control, fierceness, treachery, recklessness, conceit, and preference for personal pleasure over God—arise from within and increase as surrounding culture declines, drawing people toward practices once recognized as evil. The same heart reasserts influence among converted people, producing the Laodicean condition in which individuals declare themselves spiritually rich and in need of nothing while rejecting the continuing supply of Christ. God counters this sickness by imparting His Spirit, which supplies power, love, and a disciplined mind capable of controlling human nature. Through this gift believers are equipped to delay gratification, accept responsibility, remain dedicated to truth, and exercise wisdom, thereby maturing into the measure of the stature of the fullness of Christ and becoming fit for the responsibilities God has ordained.