The Bible makes it very clear that God doesn’t make frivolous promises. When God promises something, it is certain that the promise will be fulfilled. God promised salvation to every person who truly believes in Jesus Christ as his Lord and Savior (Rom. 10:9-13; Acts 16:30-32; John 3:16-17; 6:47; Eph. 2:8-9; Acts 13:38-39; Heb. 10:35-36). The fulfillment of God’s promise of salvation to those who believe through faith does not depend on the sinner, but on God. Salvation is a gift of grace from our loving God and nothing can interfere with this promise (Rom. 8:31-39).
Although the previous paragraph should be enough of an answer, it may be helpful to delve into this matter a little more.
Another way to answer this question lies in the Reformed doctrine of the perseverance of the saints. This doctrine holds that those whom God has effectually called and regenerated to a state of grace can never ultimately fall away from that state of grace and will never lose their eternal salvation. Reformed Calvinists stand virtually alone in this position regarding eternal salvation. In the common vernacular, it may be said that the Reformed Calvinist position is “once saved, always saved.”
The perseverance of the saints does not mean that the elect of God, those individuals chosen by God in eternity for redemption according to His plan of salvation, will ultimately be saved in the end, though they may fall from grace in the meantime. What it means is that the justified believer will never completely fall from the state of grace at any time in their lifetime and consequently lose their eternal salvation.
This doctrine does not require the sole activity of man in order to persevere. In reality, it is God who perseveres, not man because without God man could not persevere.
Once a sinner becomes a believer, God assures that he or she will persevere for the rest of his or her life. “Perseverance may be defined as that continuous operation of the Holy Spirit in the believer, by which the work of divine grace that is begun in the heart, is continued and brought to completion. It is because God never forsakes His work that believers continue to stand to the very end.”[1]
Scripture gives proofs of this doctrine. For example, “My sheep hear my voice, and I know them, and they follow me. I give them eternal life, and they will never perish, and no one will snatch them out of my hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father’s hand” (John 10:27-29). The apostle Paul wrote to the Philippians “And I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ” (Phil. 1:6). In 2 Timothy 1:12, Paul writes “for I know whom I have believed, and I am convinced that he is able to guard until that day what has been entrusted to me.” And finally, we see “The Lord will rescue me from every evil deed and bring me safely into his heavenly kingdom” (2 Tim. 4:18).
The perseverance of the saints may be inferred from other doctrines. The doctrine of election, for example, doesn’t mean that the elect may be saved but that all elect shall be saved. The covenant of redemption is where God gave His elect to His Son for Him to be their surety unto salvation. Christ paid for our sins by His redemptive act on the cross and intercedes with the elect in heaven which is an inferred assurance of our salvation. Perseverance may also be inferred from the mystical union with Christ in which we become one body with Him and it is impossible to break this union and thus frustrate the divine purpose.
When the sinner believes in Jesus Christ as his or her Lord and Savior, God justifies and counts him or her righteous and adopts him or her as his child, He gives assurance to the sinner of his or her future inheritance, salvation from God’s eternal condemning wrath and glorification in the new heaven and new earth for eternity (Eph. 1:11-14). If after God has done all of this, the sinner rejects God completely and ultimately, then God has done all that He did in vain. God failed. But we know that God has revealed to us in Scripture that He is perfect in every way and is unable to fail or do anything in vain.
If we deny the doctrine of the perseverance of the saints, then it makes our salvation subject to the will of the sinner rather than the grace of God. Therefore, once a sinner believes and is justified and adopted it is impossible for that believing sinner to lose his or her salvation (John 10:27-29; Phil. 1:6; 2 Thess. 3:3; 2 Tim. 1:12; 4:18).
[1] Louis Berkhof, Systematic Theology (The Banner of Truth Trust, 2012), 568.
