Sorry, I will be glad to post more to support my point.
1 Cor. 6:7 Actually, then, it is already a defeat for you, that you have lawsuits with one another. Why not rather be wronged? Why not rather be defrauded? 8 On the contrary, you yourselves wrong and defraud. You do this even to your brethren. 9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals, 10 nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God. 11 Such were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God.
Yes, they are Christians and are justified. Why then the warning "Do no be deceived"? Don't they already know non-Christians will not inherit the kingdom of God?
5:11 But now I am writing to you that you must not associate with anyone who claims to be a brother or sister but is sexually immoral or greedy, an idolater or slanderer, a drunkard or swindler. Do not even eat with such people.
12 What business is it of mine to judge those outside the church? Are you not to judge those inside? 13God will judge those outside. “Expel the wicked person from among you.”
How are we to know who is a Christian and who is not, by their works, good or bad.