Wormwood
Chaps
The Bible declares “the wages of sin (singular) is death.” The word in parenthesis is mine. If it only takes one sin to come under the wrath of God then ultimately, in a sense, each and every sin is a “sin unto death” and a contradiction to what you’ve alluded to as apostasy and false teaching.
I could be wrong in my understanding of “sin unto death.” Can you elaborate?
To God Be The Glory
I agree that all sin brings death. However, the context of 1 John 5 is not talking about sin in general. John is instructing these believers to not pray about a specific sin. There is a particular issue he is addressing in this letter and he is teaching these believers how to deal with this issue. Allow me to quote some sections to show you what I mean.
“Dear children, this is the last hour; and as you have heard that the antichrist is coming, even now many antichrists have come. This is how we know it is the last hour. They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us.” (1 John 2:18–19, NIV84)
“I am writing these things to you about those who are trying to lead you astray.” (1 John 2:26, NIV84)
“Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world. You, dear children, are from God and have overcome them, because the one who is in you is greater than the one who is in the world. They are from the world and therefore speak from the viewpoint of the world, and the world listens to them. We are from God, and whoever knows God listens to us; but whoever is not from God does not listen to us. This is how we recognize the Spirit of truth and the spirit of falsehood.” (1 John 4:1–6, NIV84)
More verses could be listed, but this is to give you an idea. The reason John is writing is to warn these believers about false teachers who are denying the truth about Jesus and are leading members of the congregation into false doctrine and sinful lifestyles. Moreover, John writes further about this issue in 2 John.
“Many deceivers, who do not acknowledge Jesus Christ as coming in the flesh, have gone out into the world. Any such person is the deceiver and the antichrist. Watch out that you do not lose what you have worked for, but that you may be rewarded fully. Anyone who runs ahead and does not continue in the teaching of Christ does not have God; whoever continues in the teaching has both the Father and the Son. If anyone comes to you and does not bring this teaching, do not take him into your house or welcome him. Anyone who welcomes him shares in his wicked work.” (2 John 7–11, NIV84)
So, the issue here John is referring to are these "deceivers" who twist the truth about Jesus and are "antichrists." Thus, the point John is making is that although believers can go boldly before the throne of grace and know God hears them, praying for "antichrists" is counterproductive. This is the specific sin that John references over and over in his letter and is the focus of his warnings and instruction. Thus, the "sin that leads to death" is the embrace of the message of antichrists. They "do not have God" and are false prophets who are trying to lead people astray.