Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment. And this we will do if God permits. For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, to restore them again to repentance, since they are crucifying once again the Son of God to their own harm and holding him up to contempt. (Hebrews 6:1-5a ESV)
Some will assert that the above warnings against apostasy or falling away, are addressed to believers, and imply a possibility of their falling away, or committing apostasy. Those who believe that ‘he who began a good work will bring it to completion at the day of the Lord’ (Phil 1:6), offer other purposes for the above warnings.
There is, of course, a sense in which it is possible for believers to fall away, — when they are viewed simply in themselves, with reference to their own powers and capacities, and apart from God’s purpose or design with respect to them. And it is admitted by all that believers can fall into sin temporarily.
The primary purpose of these passages, however, is to induce men to co-operate willingly with God for the accomplishment of His purposes. They are inducements which produce constant humility, watchfulness, and diligence. In the same way a parent, in order to get the willing co-operation of a child, may tell it to stay out of the way of an approaching automobile, when all the time the parent has no intention of ever letting the child get into a position where it would be injured. When God plies a soul with fears of falling it is by no means a proof that God in His secret purpose intends to permit him to fall. These fears may be the very means which God has designed to keep him from falling.
Secondly, God’s exhortations to duty are perfectly consistent with His purpose to give sufficient grace for the performance of these duties. In one place we are commanded to love the Lord our God with all our heart; in another, God says, “I will put my Spirit within you, and cause you to walk in my statutes.” Now either these must be consistent with each other, or the Holy Spirit must contradict Himself. Plainly it is not the latter.
Thirdly, these warnings are, even for believers, incitements to greater faith and prayer.
Fourthly, they are designed to show man his duty rather than his ability, and his weakness rather than his strength.
Fifthly, they convince men of their want of holiness and of their dependence upon God.
Sixthly, they serve as restraints on unbelievers, and leave them without excuse.
I would agree that left to our own devices and natural abilities & desires, we would probably be just like the Israelites who had a track record of making promises and falling away again and again and again. However, as mentioned above, spoken by the prophet Ezekiel, God had a plan. . .
And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh. And I will put my Spirit within you, and cause you to walk in my statutes and be careful to obey my rules. (Ezekiel 36:26-27 ESV)
Assuming the above to be true, solely because of God’s work in the human heart, why would we want to believe that a true Christian could fall away?