Charles Spurgeon Commentary 1 John 5:16-18

"If any man see his brother sinning a sin not unto death, he shall ask, and [God] will give him life for them that sin not unto death. There is a sin unto death: not concerning this do I say that he should make request. All unrighteousness is sin: and there is a sin not unto death. We know that whosoever is begotten of God sinneth not; but he that was begotten of God keepeth himself, and the evil one toucheth him not." — 1 John 5:16-18 (ASV)

If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it. All unrighteousness is sin: and there is a sin not unto death. We know that whatsoever is born of God sinneth not; but he that is begotten of God keepeth himself, and that wicked one toucheth him not.

He who has committed the sin which is unto death has no desire for forgiveness. He will never repent, he will never seek faith in Christ, but he will continue hardened and unbelieving; he will henceforth never be the subject of holy influences, for he has crossed over into that dark region of despair where hope and mercy never come. Perhaps some of you think that you have committed that unpardonable sin, and are at this moment grieving over it.

If so, it is clear that you cannot have committed that sin, or else you could not grieve over it. If you have any fear concerning it, you have not committed that sin which is unto death, for even fear is a sign of life. Whoever repents of sin and trusts in Jesus Christ is freely and fully forgiven; therefore, it is clear that he has not committed a sin which will not be forgiven. There is much in this passage to make us prayerful and watchful, but there is nothing here to make a single troubled heart feel anything like despair.

He who is born again, born from above, can never commit this unpardonable sin. He is kept from it; that wicked one cannot even touch him, for he is preserved by sovereign grace against this dreadful damage to his soul. You need not be curious to inquire what this unpardonable sin is. I will give you an old illustration of mine concerning it.

You may sometimes have seen a notice put up on certain estates in the country, "Man-traps and spring guns set here," but, if so, did you ever go around to the front door of the mansion and say, "If you please, will you tell me where the man-traps are, and where the spring guns are set?" If you had asked that question, the answer would have been, "It is the very purpose of this warning not to tell you where they are, for you have no business to trespass there at all." So, all unrighteousness is sin, and you are warned to keep clear of it. There is a sin unto death, but you are not told what that sin is, so that you may, by the grace of God, keep clear of sin altogether.