“And if your brother sins against you, go, show him his fault between you and him alone. If he listens to you, you have gained your brother.”
Here Jesus emphasises the responsibility that each disciple has for his ‘brother' disciple. We are all responsible for each other! We must remember that this is spoken to those who have been warned that they must be as little children in their approach to their spiritual lives, humble, lowly and not self-seeking or self-opinionated. They must be concerned not to cause another to stumble. They must be dealing sternly with sin in their own lives. They must be concerned with their Father's desire to restore any who have gone astray. It is to such that Jesus gives this task, where a brother is known to be sinning. It is thus not a charter for trying to pick holes in people or get them into trouble. We must ‘consider ourselves, lest we also be tempted' (Galatians 6:1).
And the disciple who discovers sin in another disciple will try to deal with the matter discreetly and personally. He is to go to him person to person to seek to show him his fault privately without drawing the attention of others to it. Then if he listens the brother has been ‘gained'. He can still be treated as a brother. The straying sheep has been restored. The stumbling little one has been bolstered up. The congregation is still complete. Paul describes how it is to be done, ‘in a spirit of meekness, looking to yourself lest you also be tempted' (Galatians 6:1). For there is nothing more likely to cause a man to sin than when he seeks to help another who has sinned. The danger is that he might become censorious or complacent, self-exalting or privately self-conceited, petty minded or over-magnanimous. He treads a difficult path. And the hope is that the whole matter will be dealt with lovingly and amicably, without drawing anyone else's attention to it.
One principle lying behind this is Leviticus 19:17. ‘Do not hate your brother in your heart. Rebuke your neighbour honestly so that you will not share in his guilt.' The idea is that we all have a responsibility towards each other so as to preserve the purity of God's people.
‘Against you.' The manuscripts are divided as to whether this should be in the text. Aleph, B, f1, 1582 exclude it, while D, W, Theta, f13 28 and many others include it. As it is difficult to see why it should have been excluded (unless it was being misused) the former is probably more likely. But it does not really make much difference. In either case the point is not to get one over on someone, but to honestly and genuinely, spiritually and humbly, help them in dealing with their sin. And every disciple who sins has sinned against every other disciple.
The sin in mind here is a blatant open sin whose effects are still felt, or which is still going on, and the purpose is the forgiveness of the individual and the restoration of fellowship in the discipleship circle, and the individual restoration of the disciple involved. The need for the prayerfulness of all who are involved can be assumed from Matthew 18:19.