A naughty person, a wicked man, walketh with a froward mouth.
 A false witness that speaketh lies, and he that soweth discord among brethren.
 Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them.
 And have no fellowship with the unfruitful works of darkness, but rather reprove them.
I once heard a pastor say, “a person who tries to sew division can either repent or hit the road”.
When I heard this I was taken aback, especially to hear this come from a pulpit.
For anyone trying to cause division in the church, especially when other people have a firm Biblical foundation with a shepherd, a Pastor, a Man of God that sticks to that foundation with our Lord and Savior, Jesus Christ as the cornerstone (see Isa 28:16, Eph 2:20), that person’s words should fall on deaf ear, and we shouldn’t believe them. We should be reading our Bible in order to reprove false claims and lies by following what the Word of God tells us to do.
Vine’s Complete Expository Dictionary defines reprove to convict, rebuke or to “expose”.
To totally shun this person is not what we are taught in the Bible. The Apostle Paul tells us to “mark” and “avoid” them. Remembering who they are and not fellowship with them. But we should expose and rebuke the lie, let them know why it is wrong and why we must not do it through the teaching in the Bible, and if this person has any kind of conscience, leave it to God to bring conviction upon their heart for the sin.
Matthew 18:15-17 tells us how we should handle sin amongst our brethren. At first, it should be private between you and he. If he hears and is reconciled, then you have gained a brother. If the person doesn’t understand, ask for help from two or three people from the church.  “… in the mouth of two or three witnesses, every word may be established.” If he doesn’t hear then, tell it to the church. If he still doesn’t see that he has sinned, see him as backslidden.
I’m not defending anyone who sins, but if this doctrine is followed for sinners to “repent or else leave” then half the church wouldn’t exist. John wrote, “If we say that we have no sin, we deceive ourselves, and the truth is not in us.” (1 John 1:8) Even though we try to avoid it, everyone has sinned, including myself. Even after being saved and receiving the Holy Ghost.
The Bible says not to allow bad behavior to flourish but not to immediately shun. Paul wrote in Titus, “A man that is an heretick after the first and second admonition reject; Knowing that he that is such is subverted, and sinneth, being condemned of himself. (Titus 3:10-11)”
Everyone doesn’t ask for forgiveness and see the err in their ways, first visit. Be it from not understanding the message, a presumption, or predisposition. Sometimes it takes a few services, reading the Bible, and prayer to God, for God, working through a man of God, to help someone lower the walls built, and soften the heart in order for conviction to set in for repentance to occur.
James said, “For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.” (James 2:10) Meaning, if we follow God’s law, and break one commandment we fall short of all of them. Even though we avoid sin and being cut off from God, when we realize we have sinned, we should reconcile with the person we offended and repent no matter how miniscule we think the sin we committed is. Sin is sin. Our soul is not worth risking eternal torment.