15 “Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother.
16 But if he will not hear, take with you one or two more, that ‘by the mouth of two or three witnesses every word may be established.’
17 And if he refuses to hear them, tell it to the church. But if he refuses even to hear the church, let him be to you like a heathen and a tax collector.
This teaching on forgiveness is probably tied to the teaching on humility earlier in the chapter — Don’t think you are greater than your brother; don’t do anything to cause him to sin; and, if he sins against you, forgive him.
against you (v.15) — not in some manuscripts, so the Lord could have been referring to more general sins and not just those against a given individual.
gained (v.15) —In considering our Lord’s use of the word “gained” here, it is very interesting to trace it through the New Testament. It is a commercial word, a word of the market place. It is a word which is used to characterize the processes by which a man accumulates wealth. The use of the word in this connection, so far as the sinning brother is concerned, recognizes loss. A man who has sinned is in certain senses lost; when he is restored he is gained, and the gain is interpreted by the context. — Morgan, page 232.
by the mouth of two or three witnesses … (v.16) — taken from Deuteronomy 19:15
heathen (v.17) = Gentile — more evidence that the Lord was talking to Jews only in this passage (although the principle in verses 15-17 is universal — Leviticus 19:17; Galatians 6:1; 2 Corinthians 13:1; 1 Timothy 5:19). The Lord was NOT teaching about a future institution, the Christian church. He would not have said, in essence, “After the resurrection, I will establish a church among the Gentiles. In that church, if a sinner refuses to admit his sin, treat him like a Gentile.” It’s the audience, not the principle, I’m pointing out here. Jesus was talking to a Jewish audience (His apostles) about the kingdom, although, as I’ve just mentioned, the principles also apply in the church.
church (v.17) = assembly (as always) — not referring to the still-future body of Christ church but to any assembly of believers (in the immediate context, an assembly of Jewish believers)