Question: "When should a Christian try to correct another Christian?"
Answer: This can be a delicate subject. It is wise to spend time in prayer first, to check our motivation and ask for guidance. There are times when Christians are called upon to "talk to" or try to correct a fellow Christian. Assuming we are talking about a matter of sin in a believers’ life, our motive and intent should always be to bring about repentance and restoration to the erring brother or sister in Christ.
First, our attitude is very important. "Be kind and tender to one another. Forgive each other, just as God forgave you because of what Christ has done" (Ephesians 4:32). It is then that we are more able to "speak the truth in love" (Ephesians 4:15). In his epistle to the Galatians, Paul had a similar warning about attitude: "Brothers, if someone is caught in a sin, you who are spiritual should restore him gently. But watch yourself, or you also may be tempted" (Galatians 6:1). Here we see that those who are “spiritual,” meaning walking in the Spirit in faith and obedience, should gently restore someone who is in sin, being always aware of how easily we can all be tempted by Satan who wants to ensnare everyone in his traps.
The Bible prescribes the procedure for confronting a sinning brother or sister in an extensive passage on church discipline: "If your brother sins against you, go and show him his fault, just between the two of you. If he listens to you, you have won your brother over. But if he will not listen, take one or two others along, so that ‘every matter may be established by the testimony of two or three witnesses.' If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, treat him as you would a pagan or a tax collector" (Matthew 18:15-17). Again, this is the procedure for confronting a sinning brother, not someone whose behavior you feel needs modifying in some way or someone who merely irritates or annoys you.
On a different slant, one of the most often quoted scriptures is "Judge not, lest ye be judged" (Matthew 7:1 KJV). Taken out of context, the verse has been used to incorrectly justify never taking a stand on anything that would require a judgment to be made. Rather, the verse is referring to hypocritical, self-righteous, unfair kinds of judgment, especially where the confronter is guilty of the same sin as the one being confronted.
So, when should Christians talk to or try to correct a fellow Christian? When we have talked to the Lord first, have an attitude of submission and concern for the other person, and are committed to following the procedures outlined in His Word for such a situation.