1 John 5:16

If anyone see his brother sin
Those who have such an interest at the throne of grace, and such boldness and freedom there, should make use of it for others, as well as themselves, and particularly for fallen believers; for a "brother"; not in a natural or civil sense, but in a spiritual sense, one that is judged to be born again, and belongs to the family and household of God, and is a member of a Gospel church; and so is under the watch, inspection, and care of the saints; and is observed to sin, as the best of men are not without it, nor the commission of it, in thought, word, or deed: and this sin of his is

a sin [which is] not unto death;
every sin, even the least sin, is in its own nature mortal, or deserving of death; the proper wages of sin is death, yea, death eternal; yet none of the sins of God's elect are unto death, or issue in death, in fact; which is owing not to any different nature there is in their sins, or to their good works which counterbalance them; but to the grace of God, and to the blood and righteousness of Christ, by which they are pardoned and justified, and freed from obligation to punishment, or eternal death, the just demerits of them: but how should another man know that a brother's sin is not unto death, when it is of the same nature and kind with another man's? it is known by this, that he does not continue in it; he does not live in the constant commission of it; his life is not a course of iniquity; that sin he sins is not a governing one in him; though he falls into it, he rises up out of it through divine grace, and abides not in it; and he has a sense of it, and is sorry for it, after a godly sort, loaths it, and himself for it; is ashamed of it, ingenuously confesses it, and mourns over it and forsakes it: now when any strong believer or spiritual man sees or knows that a brother has sinned, and this is his case,

he shall ask;
he shall pray to God for him, that he would administer comfort to him, discover his love, and apply his pardoning grace to him, and indulge him with his presence and the light of his countenance:

and he shall give him life;
that is, God shall give the sinning brother life; by which may be meant comfort, that which will revive his drooping spirits, and cause him to live cheerfully and comfortably, that so he may not be swallowed up with over much sorrow; or he shall grant a discovery of the pardon of his sin unto him, which will be as life from the dead, and will give him a comfortable hope of eternal life, of his right unto it, and meetness for it:

for them,
or "to them"

that sin not unto death,
as the Syriac and Arabic versions render it; for this phrase is only descriptive of the persons to whom life is given by God, upon the prayers of saints for them, and not that this life is given to him that prays, and by him to be given to the sinning person. The Vulgate Latin version renders the whole thus, "and life shall be given to him that sins not unto death"; which leaves the words without any difficulty: the Ethiopic version indeed renders it, "and he that prays shall quicken him that sins [a sin] not unto death"; and this sense some interpreters incline to, and would have with this text compared ( 1 Timothy 4:16 ) ( James 5:20 ) .

There is a sin unto death;
which is not only deserving of death, as every other sin is, but which certainly and inevitably issues in death in all that commit it, without exception; and that is the sin against the Holy Ghost, which is neither forgiven in this world nor in that to come, and therefore must be unto death; it is a sinning wilfully, not in a practical, but doctrinal way, after a man has received the knowledge of the truth; it is a wilful denial of the truth of the Gospel, particularly that peace, pardon, righteousness, eternal life, and salvation, are by Jesus Christ, contrary to the light of his mind, and this joined with malice and obstinacy; so that there is no more or other sacrifice for such a sin; there is nothing but a fearful looking for of wrath and fury to fall on such opposers of the way of life; and as the presumptuous sinners under Moses's law died without mercy, so must these despiteful ones under the Gospel; see ( Matthew 12:31 Matthew 12:32 ) ( Hebrews 10:26-29 ) . Some think there is an allusion to one of the kinds of excommunication among the Jews, called "shammatha", the etymology of which, according to some Jewish writers, is (htym Mv) , "there is death" ^F20.

I do not say that he shall pray for it;
the apostle does not expressly forbid to pray for the forgiveness of this sin, yet what he says amounts unto it; he gives no encouragement to it, or any hopes of succeeding, but rather the reverse; and indeed where this sin is known, or can be known, it is not to be prayed for, because it is irremissible; but as it is a most difficult point to know when a man has sinned it, the apostle expresses himself with great caution.