“For I am afraid that perhaps when I come I may find you to be not what I wish and may be found by you to be not what you wish; that perhaps there will be strife, jealousy, outbursts of anger, selfish ambition, slanders, gossip, arrogance, disturbances. I am afraid that when I come again my God may humiliate me before you, and I may mourn over many of those who have sinned in the past and not repented of the impurity, sexual immorality, and sensuality which they have practiced.” 2 Corinthians 12:20-21 LSB https://bible.com/bible/3345/2co.12.20-21.LSB
Who is a Christian? For most in the church, we accept a Christian as the person who claims to believe in Jesus. Yet the devil believes in Jesus. Is he, too, a Christian? What is it that a person believes that makes them a Christian? It is that God has come to live among us in the flesh to perfectly live before God as a man so that as a man, He could be sacrificed for the sins of all man on the cross.
It is that this man also rose from the dead, proving His sacrifice for the sins of all humanity was accepted by God the Father, Who has now appointed God the Son Judge and Lord over everyone because of His perfect life and sacrifice. This belief that Jesus is Judge and Lord leads us to repentance, the first words of what God requires recorded from the mouth of God when He lived among us as one of us.
The kingdom of God is at hand and is entered by humbling ourselves before God, turning from doing all those things God condemns and for which God was crucified, and turning towards all those things God commands summarized in loving Him with all of our heart, soul, mind, and strength and loving our neighbor as ourselves. Paul expected to see the church in Corinth as different from the people of Corinth.
In the church, those who believe, proven by their repentance and obedience to God, would look different from everyone else, for they would no longer live like those who do not believe and therefore have not repented. Those who genuinely believe live God’s ways as revealed in God’s word. Those who believe but have not repented of their sins are like the enemy of God. They continue to do those things that God despises and for which He died, proving that they are not truly His.