‘Like faith, unbelief is also a personal choice of the will. Unbelief is a sinners own fault. (…)
The Bible tells us to “take heed… lest there be in any of you an evil heart of unbelief” (Heb. 3:12). “Take heed” implies choice and “evil heart of unbelief” means that unbelief is not merely of the mind but is of the will. Unbelief is described as being deliberate. “For this people’s heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and should understand with their heart, and should be converted, and I should heal them” (Matt. 13:15; Acts 28:27). This shows their personal and intentional choice. Their unbelief was volitional. Men purposely turn their ears away from the truth. The Bible says, “They…stopped their ears” (Acts 7:57). And it says, “…they shall turn away their ears from the truth” (2 Tim. 4:4). Unbelievers are those who “loved darkness rather than light” (Jn. 3:19). Unbelief is the wills active state of suppressing and rejecting the truth. Unbelievers are those who “hold the truth in unrighteousness” (Rom. 1:18).
The Bible says, “Today if ye will hear his voice, harden not your hearts” (Heb. 3:15; 4:7). This command implies that a man chooses to harden his heart or not. It is a matter of our own personal choice whether we reject the word of God by hardening our hearts or if we receive the word of God by obeying in our hearts. It is something that we determine, which we have control over, which is why it is commanded of us not to harden our hearts.
We are also told in the Bible that men refused to believe in Jesus Christ. “The stone which the builders refused is become the head stone of the corner” (Ps. 118:22; Matt. 21:42; Mk. 12:10; Lk. 20:17). That means that they deliberately rejected Jesus Christ in their hearts. They decided not to embrace the truth of Jesus Christ. Just as faithfulness is obedience, faithlessness is disobedience. The Scriptures even contrast disobedience with believing. “Unto you therefore which believe he is precious, but unto them which be disobedient, the stone which the builders disallowed, the same is made the head of the corner” (1 Pet. 2:7). An unbelieving heart is a disobedient heart. It is the wills rejection of the truth that is revealed to the mind.
Jesus was frustrated with the world because of their unbelief. “He answereth him, and saith, O faithless generation, how long shall I be with you? How long shall I suffer you?” (Mk. 9:19) Why be frustrated with men for not doing what they cannot do? Why blame them for doing what they could not avoid, or blame them for not doing what cannot be done? Jesus’ frustration with that generation is justified and rational, if and only if they were capable of being a faithful generation but were choosing not to be.
Jesus even rebuked men for not believing, which implies that it is their choice to believe or not. Jesus “upbraided them with their unbelief and hardness of heart, because they believed not…” (Mk. 16:14). Jesus blamed them for their unbelief, which means that it was their own fault! And if it was their own fault, it therefore was their own free choice! It is a self-evident truth that they could not be blamed if it was not their own fault or free choice.
The Bible also says about Jesus, “Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken” (Lk. 24:25). Again, it would make no sense to rebuke men for not believing, unless faith and unbelief is their free choice. Their unbelief was their own deliberate choice, as implied in the rebuke “slow of heart to believe…” Jesus did not look at them in their unbelief and think, “Poor men. God has not yet granted them the gift of faith.” He knew that their unbelief was their own fault, not God’s fault.
We are told that Jesus “marveled because of their unbelief” (Mk. 6:6). If they were incapable of believing, or if God simply did not grant them faith, Jesus would not have marveled. There would be nothing to marvel at. Jesus marveled because they could have and should have believed, but they didn’t. Jesus even commanded men, “be not faithless, but believing” (Jn. 20:27). Therefore, it is our choice to be faithless or believing. Whether we believe or whether we are faithless depends upon us.’
Source: Jesse Morrell, “Repentance, Impenitence, Faith & Unbelief Are Free Will Choices of Men” (biblicaltruthresources).