So watch yourselves! "If another believer sins, rebuke that person; then if there is repentance, forgive. Even if that person wrongs you seven times a day and each time turns again and asks forgiveness, you must forgive." Luke 17:3-4, NLT
To rebuke does not mean to point out every sin we see; it means to bring sin to a person's attention with the purpose of restoring him or her to God and to fellow humans.
When you feel you must rebuke another Christian for a sin, check your attitudes before you speak. Do you love the person? Are you willing to forgive? Unless rebuke is tied to forgiveness, it will not help the sinning person.