We should pray earnestly for those who fall, for the Lord establishes our mutual dependence by making our prayers for each other the occasion of his restoring the erring brother or sister.
Who is meant by my brother? Can my brother sin a sin unto death? John consistently uses the term ‘brother’ for believers and assures us that all such have eternal life, and yet he admits there are those who were among us but who went out from us; they appeared to be brethren, but were not.
How do we know what the sin unto death is, and what is the prayer we should not pray?
Is it a prayer for the non-elect? No, we cannot know who they are until the end, yet we are to obey this Scripture now.
Is it any sin which God decides not to forgive? No, because the verse assures us that our prayers will result in God’s forgiveness.
Is it a sin which is not repented of? No, because we are to pray with confidence before God has given life and therefore before there has been repentance.
Is it a sin which is unforgiven at death? It may include this and certainly we may not pray for the dead, for their eternal state cannot change after they have left this world, but John expects us to discern the sin unto death while the person is still alive.
Is it a certain type of sin? Yes, for Scripture warns us there is such a sin (Matthew 12:31; Mark 3:28; Luke 12:10; Hebrew 6:6; 10:26).
Will we always recognize this sin? No, for even the disciples did not know that this sin existed before Christ taught them. Nevertheless, there is such a sin and God is careful not to create a conflict between his intention not to forgive the unforgiveable sin, and his promise that prayer for the sinning brother will be answered; he never encourages us to ask for what he has no intention of giving us. This explains the curious form of the exhortation which is cast as less than a prohibition on such prayer, just because we may fail to discern such difficult matters.