What does the Bible say if you know your sister in the church is sinning. What should you do, leave it alone or tell her?
“Brethren, if a man be overtaken in a fault, ye which are spiritual restore such a one in the spirit of meekness; considering yourself, lest you also be tempted. Bear ye one another’s burdens, and so fulfil the law of Christ.” (Galatians 6:1-2)
“Moreover, 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 they brother. But 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. And 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 and a publican.” (Matthew 18:15-17)
It is clear that we must go to a sinning sister and try to correct her privately and out of love, not spite. If that doesn’t work, take a couple of other people (perhaps leaders in the church). If they still refuse to correct their actions, then they are to be treated as one who is an unbeliever.
Two things to keep in mind. Be sure that it is truly a sin from a biblical standpoint. If they do change, make sure to welcome them back with open arms. Too often someone tries to correct another for something like smoking or drinking caffeine, neither of which are clear-cut sins. Then, when the other person objects because they can not be shown from scripture that it is a sin, hard feelings and resentment result. The other problem I have seen is that a church still holds the sin against somebody after they have repented. That’s like saying, “God will forgive you but I won’t.” We should be careful about putting ourselves above God.