“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.”
During the Protestant Reformation, the debate was never over the necessity of grace. To this day, both Roman Catholics and Protestants agree that divine grace is necessary for salvation. Neither group advocates a Pelagian view that would say that grace is helpful but not strictly necessary to be saved.
There was no real debate regarding the necessity of grace during the Reformation, but there was disagreement on the sufficiency of grace. To put the disagreement most simply, Rome said then and continues to say now that grace enables but does not compel salvation. Not everyone who receives the grace of God ends up in heaven. That is because grace in itself cannot initiate, sustain, or complete salvation without free human assent and cooperation. And since human assent and cooperation are not guaranteed by grace, many receive grace but do not persevere in faith. This understanding puts the final decision with respect to salvation in our hands. Though Roman Catholicism would not state it so crassly, its official teaching makes the human will decisive in redemption.
Magisterial Protestantism and its heirs in the Reformed tradition, however, argued for the necessity and sufficiency of grace in salvation. Grace enables and compels. Everyone to whom saving grace is shown perseveres to the end and dies in faith. Human beings act at various points in salvation, particularly in sanctification, but their salvation is not sustained by their cooperation. Rather, they continue to believe because God’s grace is effectual and guarantees perseverance. As today’s passage tells us, when the Lord initiates salvation, He always finishes what He starts (Phil. 1:6). He sustains and completes the redemption of all to whom redemption is given.
God keeps in salvation all those whom He saves. Everyone who is justified is also glorified; there is no such thing as a person who experiences conversion and justification but then falls away finally and fully from grace (Rom. 8:29–30). Many people make a false profession of faith and fall away because they were never truly saved to begin with (1 John 2:19). True, believers may succumb to significant sin. As Dr. R.C. Sproul says in his book Can I Lose My Salvation?, “Each and every Christian is subject to the possibility of a serious fall.” But he also notes that no true Christian will experience a total fall from grace. God’s grace will not let His people fall away finally. He loves us enough to guarantee our final redemption
Knowing that God will keep us in grace inspires us to work out our salvation, obeying Him as evidence that He is indeed preserving us. And when we see someone apparently fall from grace, that is our cue to pray for that person. We do not know whether God may yet restore that person, and we know that the Lord works through our prayers to accomplish His will.