Jesus says to His disciples, “If your brother trespass against thee, rebuke him; and if he repent, forgive him.” (Luke 17:3, KJV) Jesus also says not to expect thanks from God for doing those acts “which are commanded you.” (Luke 17:10) Instead, Jesus contends, you ought to “say, ‘We are unprofitable servants; we have done that which is our duty to do.'” (Luke 17:10)
“Them that sin rebuke before all, that others also may fear,” says Paul to Timothy, who is a minister of God.
In the New Testament, these are the only scriptures which direct anyone to rebuke another Christian — in both cases, the persons commanded to perform the admonishing are ministers or apostles appointed by Jesus or God the Holy Spirit. In other cases, God calls us not to judge one another. Instead we are to be gentle with each other, teaching what we know and being open to what we may learn from someone else. Jesus suggests settling with others before situations get out of hand.
Paul warns Timothy, “Rebuke not an elder, but exhort him as a father; and the younger men, as brethren; the elder women, as mothers; the younger, as sisters; with all purity.” (1 Timothy 5:1-2, KJV)
Rebukes are sharp; exhortations gentle. Rebukes are reserved for those God calls into full-time ministry, those who are specially called. Exhortations are for all Christians, as long as they are approached with care and with a loving spirit.