In Hebrews 3:12, churchgoers were forewarned, “Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.”
Everyone in the church is admonished to see to it that he has no evil heart. It is with brotherly love that such an admonition is given. The author of Hebrews addressed them as “brethren” to show that his admonition is given, not out of any hard feelings or distrust or jealousy, but rather out of a loving care for their spiritual safety.
What does “an evil heart of unbelief ” imply? It implies negligence and rejection of divine truths while pursuing sin. Such a heart would not submit to the claims of the Gospel of Christ. Indifference to the grace exhibited in the Gospel would be apparent. It would refuse the application of the Gospel truths to itself. That is the ultimate sign of unbelief. Just as it is by faith that a person receives Christ as his Saviour and Lord, it must also be asserted that it is a vivid manifestation of unbelief if one rejects Him. As submission to Christ’s righteousness is the greatest act of faith, rejection of His righteousness is conversely the greatest act of unbelief.
Some openly reject Christ and scorn His Word. Others do so secretly by merely paying lip service in their profession of faith. Their profession of faith is employed only as a cloak for their sins. While they claim to have given their hearts to Christ, they continue to yield themselves to hidden lusts lurking in their hearts. Their natural inclination is to sin, as sin reigns in them. It is impossible for unrestrained love for sin and faith in the Saviour to thrive in the same heart. While faith in Christ leads to sanctification, unbelief paves the way to more sins.
In an evil heart of unbelief, love for the world and for its pleasures, riches, honours always supersede the eternal things of God’s kingdom. In such a heart of unbelief, spiritual matters are deemed unworthy of its pursuit. Loss of material gain or comfort for Christ’s sake will not be tolerated, as it glories in the things of the world more than the things of Christ.
Such an evil, unbelieving heart will inevitably depart from the living God. Apostasy (or departure from God) first exists in one’s heart, and then is manifested in one’s life. Apostasy finally exposes the prideful, self-willed heart of an individual. Such departing from the living God is an immense evil and the greatest insult to God! It is the worst tragedy one can bring upon oneself. So brethren, be vigilant against the apostasy of your hearts.