Charles Spurgeon Commentary 1 John 5:16-17

"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." — 1 John 5:16-17 (ASV)

If anyone sees his brother sin a sin which is not to death, he shall ask, and he shall give him life for those who sin not to death. There is a sin to death: I do not say that he shall pray for it. All unrighteousness is sin: and there is a sin not to death.

There are multitudes of such sins; but there is a place, beyond which, if a man passes in sin, he becomes from then on dead and utterly insensible; and he will never be made alive and never be saved. If we knew a man to be in such a condition as that, the apostle's words would apply to such a case. I do not say that he shall pray for it.

But, as we cannot tell that anyone is in that condition, it is well for us to ask for grace to be able to pray for every sinner, however great his sin may be. We know that all unrighteousness is sin: and there is a sin not to death.