The Israelites drove out the original inhabitants of the land. God said: they shall not dwell in thy land, lest they make thee sin against me. (Exod 23:33) This reason retains validity in the church age. As sin may spread to contaminate other members of the church, some sinners must be expelled from the church.
And so Paul writes: know you not that a little leaven leaveneth the whole lump? Purge out therefore the old leaven. (1 Cor 5:6,7) When someone in the Corinthian church had his father’s wife, probably his step mother, they were told: put away from among yourselves that wicked person. (1 Cor 5:13)
Not only for gross sin, but also for lesser sin, sinners were to be excluded. Paul wrote to the church: you must not associate with anyone who calls himself a brother but is sexually immoral or greedy, an idolater or a slanderer, a drunkard or a swindler. With such a man do not even eat. (1 Cor 5:11 NIV) One would assume that Paul is referring, not to an isolated fault, but to a life given to these vices; for example being greedy to the point of dishonest gain.
(For lesser faults such as: some who walk among you disorderly, working not at all, but are busybodies, (2 Thess 3:11) there was a lesser punishment than complete exclusion. Paul wrote: if any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed. Yet count him not as an enemy, but admonish him as a brother. (2 Thess 3:14,15) Such a one was permitted to come to church, being treated like a brother, but was excluded from close fellowship.)
Returning to the case of more serious sin, when a believer is totally excluded from Christian fellowship by church judgement, he is no longer protected by God. Such a one is delivered: unto Satan for the destruction of the flesh. (1 Cor 5:5) This destruction, perhaps by sickness, is a chastening, and is supposed to bring repentance: that the spirit may be saved in the day of the Lord Jesus.
In addition to the man who had his step mother, Paul delivered unto Satan some: that they may learn not to blaspheme. (1 Tim 1:20)
If we know of serious sin being committed in the church, it is our duty to take action, eventually reporting them to the pastor. Bearing true witness cleanses the environment of the church.
The methodology of dealing with sin against another is explained by Jesus is Matthew 18. But this passage also has application for sin against God. Firstly, Jesus said: if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother. (Matt 18:15) You may have saved a soul from death and may have covered a multitude of sins (James 5:20).
Secondly, Jesus said: if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established. (Matt 18:16) Thirdly, Jesus said: if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man. (Matt 18:17) Thus the sinner is normally given three opportunities to repent before excommunication.
When a person is excommunicated by the church, God stands with the church’s judgement. In this context Christ said: Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven. Again I say unto you, That if two of you shall agree on earth as touching anything that they shall ask, it shall be done for them of my Father which is in heaven. (Matt 18:18,19) The binding or the loosing is from Satan’s power.
An excommunicated person can be received back into the church after repentance. Paul says of such a person: Sufficient to such a man is this punishment, which was inflicted of many. So that contrariwise ye ought rather to forgive him, and comfort him, lest perhaps such a one be swallowed up with overmuch sorrow. (2 Cor 2:6,7)
The presence of abominations in the church causes God to: go far off from his sanctuary. (Ezek 8:6) Jesus has something against the whole church if wickedness is harboured. He said to the church in Smyrna: I have a few things against thee, because thou hast there them that hold the doctrine of Balaam, who taught Balac to cast a stumblingblock before the children of Israel, to eat things sacrificed unto idols, and to commit sexual immorality . . . Repent; or else I will come unto thee quickly and will fight against them with the sword of my mouth. (Rev 2:14,16) Christ’s sword is the same as that with which slays the armies of the antichrist (Rev 19:21)
We should not be deterred from judging in the church by the vast numbers of those who may harbour the wicked. Benjamin, one of the tribes of Israel, was, according to God’s command, almost totally wiped out, because they harboured a pack of sodomites who had raped a woman. (Judges 19:22-20:48)
The New Testament equivalent of destroying a tribe in Israel, is to cut off communications with denominations which harbour sodomites. When the righteous realise that they are excluded from other Christian fellowship because of the doctrine of their leaders, they will realise the seriousness of sin, and many will leave. It is very unpleasant and quite ridiculous to have in the midst of a godly people, those who are worse than the heathen.
When God, by famine, chastened the land of Israel, King David inquired of God for the reason: And the Lord answered, It is for Saul, and for his bloody house, because he slew the Gibeonites. (2 Sam 21:1) After the guilty men were hung: God was intreated for the land. (2 Sam 21:14) Today proponents of, and those who practice, abortion must be expelled from the church.
Now to the matter of the resolution of civil disputes between Christians. Paul writes: Dare any of you, having a matter against another, go to law before the unjust, and not before the saints? (1 Cor 6:1) Such matters should be settled within the church. As they had sought to the heathen outside the church, Paul asks them: Is it so that there is not a wise man among you? no, not one that shall be able to judge between his brethren? (1 Cor 6:5) Paul even says, that rather than bring God to shame before heathen courts, it is better: to suffer yourselves be defrauded. (1 Cor 6:7)