During the week of Passover, Jews could not have yeast at home, because it symbolized sin.
The lamb symbolized Christ: He was sacrificed for those who trust in Him.
In His home here in the world, the church, we cannot allow "old yeast", which are believers who are still living in the practice of sin, evil and malice: if left, the Church, where sincerity and truth must reign, will be totally contaminated.
A person who, claiming to be a brother, is a fornicator, or avaricious, or idolater, or abusive, or a drunkard, or rapacious should not participate in the communion of the Church: he must be delivered to Satan for the destruction of the flesh that the spirit may be saved on the day of the Lord Jesus.
In each believer his new spirit must fight against the flesh (the old nature) with the power of the Holy Spirit which is given to him when born again.
If, however, a believer wants to continue living in the flesh, he quenches the Holy Spirit and his spirit will only be saved on the day of the Lord Jesus, after the destruction of his flesh by Satan (his physical death). In this way, he remains on Earth without enjoying the blessings of communion with God until he dies.
R David Jones
1 It is actually reported that there is sexual immorality among you, and such sexual immorality as is not even named among the Gentiles—that a man has his father's wife!
2 And you are puffed up, and have not rather mourned, that he who has done this deed might be taken away from among you.
3 For I indeed, as absent in body but present in spirit, have already judged (as though I were present) him who has so done this deed.
4 In the name of our Lord Jesus Christ, when you are gathered together, along with my spirit, with the power of our Lord Jesus Christ,
5 deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus.
6 Your glorying is not good. Do you not know that a little leaven leavens the whole lump?
7 Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us.
8 Therefore let us keep the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.
9 I wrote to you in my epistle not to keep company with sexually immoral people.
10 Yet I certainly did not mean with the sexually immoral people of this world, or with the covetous, or extortioners, or idolaters, since then you would need to go out of the world.
11 But now I have written to you not to keep company with anyone named a brother, who is sexually immoral, or covetous, or an idolater, or a reviler, or a drunkard, or an extortioner—not even to eat with such a person.
12 For what have I to do with judging 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 YOURSELVES THE EVIL PERSON."
1 Corinthians chapter 5