@1stCenturyLady now to the sins that cause death and those that do not....and of those who are brought back to their old self as they shake off the experience of trying out the Christ for a spell.
First then, I do not see a spirit-filled Christian casting out demons and going back into lawlessness any where in scripture. And the scripture of Matthew 7:19-23 does not address this at all. Unless there is a missing link that points to the unfruitful tree or branch.
The sin that causes death is not spoken about in any depth or detail in scripture.
My take on it..
(1Jn 5:13) I write these things to you who believe in the name of the Son of God, that you may know that you have eternal life.
(1Jn 5:14) And this is the boldness which we have toward him, that, if we ask anything according to his will, he hears us.
(1Jn 5:15) And if we know that he hears us in whatever we ask, we know that we obtain the requests we have asked of him.
(1Jn 5:16) If anyone sees his brother sinning a sin not unto death, he shall ask and God will give him life for them that sin not to death. There is a sin unto death. Not concerning this do I say that he should make requests.
(1Jn 5:17) All unrighteousness is sin, and there is a sin not unto death.
(1Jn 5:18) We know that whoever is begotten of God does not keep on in sin; but he that was begotten of God keeps himself, and the evil one touches him not.
(1Jn 5:19) We know that we are of God, and the whole world lies in the power of the evil one.
(1Jn 5:20) And we know that the Son of God came, and has given us an understanding so that we truly know him that is true; and we are in him that is true, in His Son Jesus Christ. This is the true God and eternal life.
(1Jn 5:21) Little children, guard yourselves from idols.
So the context and audience of this subject are to believers in the Son of God who are being saved to eternal life.
It is encourages to pray for anything that God approves of and he will hear us.
Then suddenly, John plunges into sins that do not cause or does not lead to death. To pray for these (I would think even for unbelievers) that commit this type of sin and God will either sway them to the gospel or reinstate them back to life of being saved. I wonder what happens if they do not see this sin in a brother who is a believer? Of course the Spirit will convict him or her of this sin regardless....
And then he says there is a sin that leads to death. And he suggests no one pray for someone with this type of deadly sin.
Up to this point, I would now think that the use of the term 'brother' is much broader in meaning as in a seeker or even an unbeliever, that God only has to deal with and no one else. And this person who may have committed a sin that leads to death was not being saved either.
Adding to relevance to my point here, in verse 18, John reinforces the fact that (only..my input) whoever is born of God does not keep sinning,, and I would think he means those that do not lead to death as well, let alone those that cause spiritual death.
And in verse 19, John links a sinner of sin that causes death to the evil one influencing them in life. This is not usually the case with a true believer.
And so at this point I conclude that the sins that cause death are of an unbeliever only, influenced by evil and its power. So I would think these sin conspire against a believer, Christ and God directly, and they are not sins like committing habitual murder or whoredom etc., without any control.