There are those who say that "once you are saved you are always saved". They say that it is impossible to fall from God’s grace regardless of what you do. This may sound good and comforting, but let’s see what the Bible says. In 1 Corinthians 9:27 the apostle Paul says, "But I buffet my body and bring it into subjection, lest, when I have preached to others, I myself should be a castaway." Paul said that it was possible for him to become a castaway. If Paul became a castaway he would be lost.
In 1 Corinthians 10:12 Paul gives a warning to the Christians at Corinth by saying, "Therefore let him who thinks he stands take heed lest he fall." Why such a warning if it is impossible to fall? So the very people, who think they cannot fall, are given a warning to take heed lest they fall.
In Galatians 5:4 we read, "You have become estranged from Christ, you who attempt to be justified by the law; you have fallen from grace." Isn't it strange, that people who say they believe the Bible also say that we cannot fall from grace, when the Bible so plainly says that we can fall from grace. Who are we to believe, God or man? Even though many religious bodies say that you cannot fall from grace, the Bible clearly says that people can fall from grace. And without God’s grace we cannot be saved.
The doctrine of "once saved always saved" and that you cannot fall from God’s grace and be lost is a doctrine that originated with Satan. Satan wants people to believe that they cannot fall from grace and be lost. In Genesis 2:17 God told Adam and Eve not to eat of the tree of the knowledge of good and evil, and the day they ate of it they would surely die. But in Genesis 3:4 Satan told Eve, "You will not surely die". Satan only added the word "not" to what God had said. Just as Satan told a lie to Eve, Satan is still deceiving people today by telling them they can NOT fall from grace and once they are saved, they are always saved. He is trying to lull people into complacency. This is one of the many ways that Satan deceives people so they will be eternally lost. But 2 Peter 1:10 says, "be even more diligent to make your call and election sure."
God's promises are conditional upon our doing His will. Jesus says in Matthew 7:21, "Not everyone who says to Me, Lord, Lord, shall enter the kingdom of Heaven, but he who does the will of My Father in Heaven." And also Hebrews 5:9 says concerning Jesus that "He became the author of eternal salvation to all who obey Him."