The Corinthians should have known better. Paul had previously written to them on this very subject, but they had apparently misunderstood him:
“I wrote you in my letter not to associate with immoral people; I did not at all mean with the immoral people of this world, or with the covetous and swindlers, or with idolaters; for then you would have to go out of the world. But actually, I wrote to you not to associate with any so-called brother if he should be an immoral person, or covetous, or an idolater, or a reviler, or a drunkard, or a swindler—not even to eat with such a one”. I Cor. 5:9-11
Realizing the far-reaching effects of such lack of discernment by the church, Paul had good reason to question, not only the salvation of one immoral Corinthian church member, but the salvation of others within the same church. There was strife, factions and jealousy (1 Cor. 1:10-12; 3:1-4). For those who have just been born again, these can be indications of spiritual babyhood, due primarily to lack of knowledge of God's will. Until now, the Corinthians had only been fed the milk of God's Word (1 Cor. 3:2). So Paul informed them how their selfishness displeased God, expecting that they, now enlightened to the truth, would repent.
Paul taught those who truly receive by faith God's gracious gift of salvation are transformed by His Holy Spirit. Because of His wonderful work in their lives, they become holy and continue to grow holier. They are born again, and the power of sin is broken over their lives. Christ lives in them. They become new creations. No longer are their lives characterized by the practice of sin. Certainly, true believers sometimes still do sin, but they no longer practice it.
As the apostle John wrote:
“If we say that we have no sin, we are deceiving ourselves, and the truth is not in us. If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness....No one who is born of God practices sin, because His seed abides in him; and he cannot sin, because he is born of God” 1 John 1:8-9; 3:9.
The salvation that comes through Jesus Christ not only provides forgiveness of sin, it provides deliverance from sin
Thus, the true test of our faith is our behavior. And that is why Paul warns us, admonishing us to examine our lives to determine if our faith and salvation are bogus. Again, our works do not earn us salvation; our works prove that we possess true saving faith and the indwelling Holy Spirit.
“You can be sure that no immoral, impure, or greedy person will inherit the Kingdom of Christ and of God. For a greedy person is an idolater, worshiping the things of this world.
Don’t be fooled by those who try to excuse these sins, for the anger of God will fall on all who disobey him.” Eph. 5:5-6 NLT
Although it is certainly possible for a born-again person to reluctantly and temporarily stumble into one or more of these various sins, no true believer will practice these sins.
His life is characterized by righteousness, not unrighteousness, because he has submitted to the Lord from his heart, and his spirit has been re-created by the Holy Spirit.
Paul wrote, "Test yourselves to see if you are in the faith." Notice the word “IF”. That indicates the possibility that they were not "in the faith." Paul did not say, "Test yourselves and you will see that you are in the faith, because I'm very confident of your salvation."
Is this not a clear indication that Paul believed the sure possibility existed that some of them might fail the test?
It was obvious that Jesus lived in Paul and Timothy, but it was not so obvious that Jesus lived in all the Corinthians who professed to believe in Him.
God does not want our offerings; He does not want our sacrifices; He wants our desire to obey; He wants our hearts; He wants us. “Not everyone who says to me ‘Lord, Lord’ will enter the kingdom of heaven, but only he who does the will of my Father” because that is the desire of His heart. (Matt. 7:21)
King David was a man after God’s own heart because He wanted to do God’s will even though he often failed to obey.
The difference between true belief that leads to salvation and belief that falls short of salvation has to do with our devotion to the truth.
“The pride of your heart has fooled you. You live in the holes of the rock. Your home is high in the mountains. And so you say in your heart, ‘Who will bring me down to the ground?” Obadiah 1:3 NLT