I Jn. 5:16-18 is one of the scriptures people often wrestle with the understand. V. 16 “If anyone sees his brother sinning a sin which does not lead to death, he will ask, and He will give him life for those who commit sin not leading to death. There is sin leading to death. I do not say that he should pray about that. All unrighteousness is sin, and there is sin not leading to death. We know that whoever is born of God does not sin; but he who has been born of God keeps himself, and the wicked one does not touch him.

We have a number of statements and examples of God judging by removing people by death. We know that continuing in sin leads to death

Annaias and Sapphirra in Acts 5 had a sin leading to death; they lied to the Holy Spirit. This was a one time event and we do not see this repeat itself with any other apostle or in church discipline.

Heb. 3:17-19 “Now with whom was He angry forty years? Was it not with those who sinned, whose corpses fell in the wilderness? And to whom did He swear that they would not enter His rest, but to those who did not obey?” So we see that they could not enter in because of unbelief that was intentional, it was rebellious.

Rom 6:16: “Do you not know that to whom you present yourselves slaves to obey, you are that one's slaves whom you obey, whether of sin leading to death, or of obedience leading to righteousness?”

V.:22-23 “But now having been set free from sin, and having become slaves of God, you have your fruit to holiness, and the end, everlasting life. For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.” Here Paul juxtaposes life and death.

Forsaking the truth can lead one to physical judgment. James 5:19-20 “Brethren, if anyone among you wanders from the truth, and someone turns him back, let him know that he who turns a sinner from the error of his way will save a soul from death and cover a multitude of sins.”

If one continues in their sin especially as they represent the lord, God can judge them and take them home.

2 Tim 2:20-21 “But in a great house there are not only vessels of gold and silver, but also of wood and clay, some for honor and some for dishonor. Therefore if anyone cleanses himself from the latter, he will be a vessel for honor, sanctified and useful for the Master, prepared for every good work.” One can become fruitful where they were barren, without good works prone to sin.

Taking communion in a non introspective manner led to those in the early church being judged, even losing their lives. 1 Cor. 11:29-32 “For he who eats and drinks in an unworthy manner eats and drinks judgment to himself, not discerning the Lord's body. For this reason many are weak and sick among you, and many sleep. For if we would judge ourselves, we would not be judged. But when we are judged, we are chastened by the Lord, that we may not be condemned with the world.”

Again I Jn. 5:16 “If anyone sees his brother sinning a sin which does not lead to death, he will ask, and He will give him life for those who commit sin not leading to death.” One can sin and it not lead to death, the judgment from the Lord. But “There is sin leading to death. I do not say that he should pray about that.”

In other words one can pray for those who commit sin that does not lead to death and God will deliver the person, but for the one who sins that leads to death prayer will not do this.

We know that continual unbelief leads to judgment, but this specifically involves a brother, one who is part of the body of Christ. Apart from these many examples there is no definitive action one can point out and say this is the one sin that leads to death. So we should take all of these into account as God knows our heart better than we do.