The apostle Paul said in 1 Corinthians 15:2, “if ye keep in memory what I preached unto you, unless ye have believed in vain.” This is not a warning against true believers losing their salvation. This is a warning against a non-saving faith. It is only by God’s power that anyone is saved, and it is only by God’s power that anyone is kept saved. A believer's salvation is secure because Christ is holding fast to the believer, not because the believer is holding on to Christ. There are many people who acknowledge Christ. They believe in the historicity of Jesus, but they do not receive Him as Lord and Savior. Therefore, they are still lost in their sins. You believe in Jesus? That’s good, but even the demons believe in God (James 2:19).
The scary truth is that not everyone who says, “Lord, Lord shall enter into the kingdom of heaven” (Matthew 7:21). Not all who claim to believe the gospel have saving faith. Jesus repeatedly spoke of bogus believers. In the parable of the sower (Matthew 13:1-23), Jesus spoke of seed falling on stony soil and at first it appeared that something was growing, but before long the plant dried up and withered away. In other words, there are those who have an immediate, emotional response to the gospel at some point in their lives but they do not produce fruit. They have a non-saving faith. Jesus said that among the wheat (real believers) there are tares (false professors) (Matthew 13:24-30; 34-43). Jesus spoke of houses without foundations (Matthew 7:24-27), of virgins without oil for their lamps, and of gates and paths that seem right but that ultimately lead to destruction (Matthew 7:13-14). There is a faith that is not genuine; there is a faith that is vain (empty).
The key to knowing whether faith is genuine or vain is by perseverance. The truly saved are not only saved by faith but they continue to “live by faith” (Hebrews 10:38). Obedience and continuous faithfulness are markers of genuine saving faith. Those who forsake Christ and His church prove that they never really belonged to Him or it. 1 John 2:19, “They went out from us, but they were not all of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all us.” Those who continue with the Lord, prove the genuineness of their faith. Jesus said, “If you continue in my word, then are ye my disciples indeed” (John 8:31).
Back in 1 Corinthians 15:2 Paul says that those who “keep in memory” are those who have saving faith. The Greek word translated “keep” means "to hold fast; to hold firmly”. Holding on to God, holding on to the gospel is not what saves or keeps an individual saved, but it is what proves genuine salvation. Holding firmly gives evidence that one is firmly held.
My sheep hear my voice, and I know them, and they follow me: And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand. I and my Father are one. - John 10:27-30...For I the LORD thy God will hold thy right hand, saying unto thee, Fear not; I will help thee. - Isaiah 41:13
A believer holds on to Christ, because Christ is holding on to him, and genuine saving faith is marked, not by perfect obedience or faithfulness, but by a general pattern of obedience and continuous faithfulness. On this side of glory the gospel transformation does not bring about perfection but it does change the direction of one's life and actions.