I wrote to you in the epistle not to mix with fornicators, not meaning complete dissociation from the fornicators of this world or greedy and swindlers or idolaters, since you would have to then go out from the world. But now I wrote to you not to mix with anyone who is called a brother if he is a fornicator or a greedy man or an idolater or a reviler or a drunkard or a swindler. Do not eat with such a man. For what do I have to do with the judging of outsiders? Is it not the ones within you are to judge? But the ones outside God judges. Remove the evil man from among yourselves. 1 Corinthians 5:9–13, translated from the NA28 Greek text
Ἔγραψα ὑμῖν ἐν τῇ ἐπιστολῇ μὴ συναναμίγνυσθαι πόρνοις, οὐ πάντως τοῖς πόρνοις τοῦ κόσμου τούτου ἢ τοῖς πλεονέκταις καὶ ἅρπαξιν ἢ εἰδωλολάτραις, ἐπεὶ ὠφείλετε ἄρα ἐκ τοῦ κόσμου ἐξελθεῖν. νῦν δὲ ἔγραψα ὑμῖν μὴ συναναμίγνυσθαι ἐάν τις ἀδελφὸς ὀνομαζόμενος ᾖ πόρνος ἢ πλεονέκτης ἢ εἰδωλολάτρης ἢ λοίδορος ἢ μέθυσος ἢ ἅρπαξ, τῷ τοιούτῳ μηδὲ συνεσθίειν. τί γάρ μοι τοὺς ἔξω κρίνειν; οὐχὶ τοὺς ἔσω ὑμεῖς κρίνετε; τοὺς δὲ ἔξω ὁ θεὸς κρινεῖ. ἐξάρατε τὸν πονηρὸν ἐξ ὑμῶν αὐτῶν. 1 Corinthians 5:9–13, NA28
As the true Gospel is proclaimed with power, it is always accompanied by the Law which is used by the Holy Spirit to reveal to the lost their utter need for a Saviour and the complete helplessness to save themselves from the coming wrath of God upon all sin that has not been covered by blood of Christ through his atoning work on the Cross. Those who have not been justified by faith alone through grace alone, through believing the Gospel and receiving Christ as Lord and Saviour, are those mentioned in the passage above that are “outsiders.” He also makes it clear that many are “called a brother,” but their actions of an unrepentant lifestyle reveal that they are subject to being judged according to church discipline and cast out of the local body of believers.