Can you explain what the "sin unto death" mentioned in 1 John 5 is?
First, good for you. There is a command NOT to do something in that passage, and it's real hard to obey if you don't understand.
1Jn 5:15 And if we know that He hears us in whatever we ask, we know that we have the requests which we have asked from Him. 16 If anyone sees his brother committing a sin not leading to death, he shall ask and God will for him give life to those who commit sin not leading to death. There is a sin leading to death; I do not say that he should make request for this. 17 All unrighteousness is sin, and there is a sin not leading to death.
Second, it is always best to let the word of God explain for itself.
The first concept is that the only ones assured of receiving judgment from God NOW, on this earth, are those that are truly His kids. If you can live in sin and rebellion to God and not see His judgment, you NEVER WERE His kids in the first place:
Heb 12:3 For consider Him who has endured such hostility by sinners against Himself, so that you will not grow weary and lose heart. 4 You have not yet resisted to the point of shedding blood in your striving against sin; 5 and you have forgotten the exhortation which is addressed to you as sons, "MY SON, DO NOT REGARD LIGHTLY THE DISCIPLINE OF THE LORD, NOR FAINT WHEN YOU ARE REPROVED BY HIM; 6 FOR THOSE WHOM THE LORD LOVES HE DISCIPLINES, AND HE SCOURGES EVERY SON WHOM HE RECEIVES." 7 It is for discipline that you endure; God deals with you as with sons; for what son is there whom his father does not discipline? 8 But if you are without discipline, of which all have become partakers, then you are illegitimate children and not sons. 9 Furthermore, we had earthly fathers to discipline us, and we respected them; shall we not much rather be subject to the Father of spirits, and live? 10 For they disciplined us for a short time as seemed best to them, but He disciplines us for our good, so that we may share His holiness. 11 All discipline for the moment seems not to be joyful, but sorrowful; yet to those who have been trained by it, afterwards it yields the peaceful fruit of righteousness. 12 Therefore, strengthen the hands that are weak and the knees that are feeble, 13 and make straight paths for your feet, so that the limb which is lame may not be put out of joint, but rather be healed.
Notice the efforts we are to go to, to keep ourselves free from sin. (vs.4) Also note the wording in verse 13... it hints at the consequences for NOT doing what it takes to fix areas that are sin in our own lives. But that's just a hint... Then we have:
1Co 11:27 Therefore whoever eats the bread or drinks the cup of the Lord in an unworthy manner, shall be guilty of the body and the blood of the Lord. 28 But a man must examine himself, and in so doing he is to eat of the bread and drink of the cup. 29 For he who eats and drinks, eats and drinks judgment to himself if he does not judge the body rightly. 30 For this reason many among you are weak and sick, and a number sleep. 31 But if we judged ourselves rightly, we would not be judged. 32 But when we are judged, we are disciplined by the Lord so that we will not be condemned along with the world.
This makes it really clear. Verse 32 tells us the difference between those that aren't His and those that are. The world will be judged ... after they die. What is the reason that we receive our consequences now? It is so that we don't have to go through that second judgment, right? If we judge ourselves rightly, and correct our course on our own, as Christians, then God doesn't have to step in and do anything. We are self-correcting ... as we should be. Those that are true Christians (See the previous Hebrews passage) that refuse to judge themselves, and get free from the major sins are then judged by God. The consequences are in verse 30: Weakness, Sickness and "sleeping". And no, that's not getting to take a nap or receiving a cure for your sleep apnea. You have heard of the term sleeping with the fishes ... same thing:
1Th 4:13 But we do not want you to be uninformed, brethren, about those who are asleep, so that you will not grieve as do the rest who have no hope. 14 For if we believe that Jesus died and rose again, even so God will bring with Him those who have fallen asleep in Jesus. 15 For this we say to you by the word of the Lord, that we who are alive and remain until the coming of the Lord, will not precede those who have fallen asleep. 16 For the Lord Himself will descend from heaven with a shout, with the voice of the archangel and with the trumpet of God, and the dead in Christ will rise first. 17 Then we who are alive and remain will be caught up together with them in the clouds to meet the Lord in the air, and so we shall always be with the Lord. 18 Therefore comfort one another with these words.
In both these passages, the wording of sleeping or falling asleep is pretty much what the transition of leaving this life to be with the Lord will be ... for EVERY true Christian. Even those whose refusal to judge themselves correctly and correct their own path / lives for themselves will still "Sleep". They just get "taken home" sooner rather than later.
Keep in mind that while this does "seem" harsh, these people are receiving their judgment NOW and are going to heaven to be with the Lord. Same sleep we will all endure eventually... unless we remain for the end of that 1 Thessalonians passage.
Remember, those that aren't really His Kids (Christians) can "leave" the church and live like hell and never see any consequences at all.
1Jn 2:19 They went out from us, but they were not really of us; for if they had been of us, they would have remained with us; but they went out, so that it would be shown that they all are not of us.
Remember, they get judged later ... after death. So the question remains, are there any examples where someone's sins were so grievous that God decided to take destroy their physical lives and take them home now?
1Co 5:1 It is actually reported that there is immorality among you, and immorality of such a kind as does not exist even among the Gentiles, that someone has his father's wife. 2 You have become arrogant and have not mourned instead, so that the one who had done this deed would be removed from your midst. 3 For I, on my part, though absent in body but present in spirit, have already judged him who has so committed this, as though I were present. 4 In the name of our Lord Jesus, when you are assembled, and I with you in spirit, with the power of our Lord Jesus, 5 I have decided to deliver such a one to Satan for the destruction of his flesh, so that his spirit may be saved in the day of the Lord Jesus.
Notice the consequences in verse 5. Destruction of the flesh = physical death. Do they lose their salvation for refusing to judge themselves correctly and correct their own path? Nope. Their soul will still be saved even though their sin is "unto death".
Can you think of any others who God judged right now (Which makes them His kids according to Hebrews and 1 Cor.11, right?) How about Ananias and Saphira? Were they judged while still on the earth or after they died with the rest of the lost? Now, right?
So let's look at the passage in question again:
1Jn 5:15 And if we know that He hears us in whatever we ask, we know that we have the requests which we have asked from Him. 16 If anyone sees his brother committing a sin not leading to death, he shall ask and God will for him give life to those who commit sin not leading to death. There is a sin leading to death; I do not say that he should make request for this. 17 All unrighteousness is sin, and there is a sin not leading to death.
Some key points: While all unrighteousness is sin, the vast majority do not call for death(vs. 17)
Prayer is very powerful and can sway the opinion of God, and effect the outcome of what God wants to do, even with those who are such a bad influence, those who are destroying His church, those hurting His kids ... If we keep praying that God will "turn" and cause to repent, someone who has set their will against God, even as Christians, we can get in the way of God's taking them home. This is something we are commanded NOT to do. But there are levels... perhaps they are just sick/weak right now, but it could get worse because they are Christians who haven't been judging themselves correctly. What then?
Jas 5:14 Is anyone among you sick? Then he must call for the elders of the church and they are to pray over him, anointing him with oil in the name of the Lord; 15 and the prayer offered in faith will restore the one who is sick, and the Lord will raise him up, and if he has committed sins, they will be forgiven him. 16 Therefore, confess your sins to one another, and pray for one another so that you may be healed. The effective prayer of a righteous man can accomplish much. … 19 My brethren, if any among you strays from the truth and one turns him back, 20 let him know that he who turns a sinner from the error of his way will save his soul from death and will cover a multitude of sins.
Understand that just asking for the elders "could" be a sign of repentance. If it is, there is a chance that their physical ailments could be cured. If they never were real Christians and God wakes them up in this way, they can end up saved and be forgiven a multitude of sins (vs. 20) Not everyone who professes to be Christian is a real Christian. Not everyone sick and/or weak, or who dies as a Christian, is practicing severe sin either. We will all get sick, weak and die unless the Lord comes first.
Hopefully all this makes sense. If not, let me know.