1 It is reported commonly that there is lewdness among you, and such lewdness as is not so much as named among the Gentiles, that one should have his father's wife. 2 And you are puffed up and have not rather mourned so that he who has done this deed might be taken away from among you.
3 For I truly, as absent in body, but present in spirit, have already as though I were present judged concerning him who has thus done this deed. 4 In the name of our Lord Jesus Christ, when you are assembled with my spirit and with the power of our Lord Jesus Christ, 5 Deliver such a one to Satan for the destruction of the flesh so that the spirit may be saved in the day of the Lord Jesus.
6 Your boasting is not good. Do you not know that a little leaven leavens the whole lump? 7 Therefore, cleanse out the old leaven so that you may be a new lump, as you are unleavened. For even Christ our passover is sacrificed for us. 8 Therefore, let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.
9 I have written to you in this epistle not to associate with persons guilty of lewdness— 10 Yet not altogether with lewd persons of this world, or with the covetous, extortioners, or with idolaters, for then you would have to go out of the world. 11 But now I have written to you not to keep company, if any man who is called a brother is a lewd person, covetous, an idolater, a railer, a drunkard, or an extortioner. Do not even eat with such a person. 12 For what have I to do to judge those also who are outside? Do you not judge those who are inside? 13 But those who are outside God judges. "Therefore, put away from among yourselves that wicked person."
[v.6-8] - In these verses, Paul is providing some application for the removal of leaven from bread during the feast of unleavened bread following the Passover (Exodus 12:14-20. Furthermore, he tells us that Christ is our Passover lamb, who was sacrificed for us. His sacrifice, the shedding of His blood, made the way for the redemption of God's elect (Hebrews 10:10; 1st Peter 1:18-19).
[v.6] - Reference, Galatians 5:9.
[v.13] - Quoting Deuteronomy 17:7 (LXX).