Actually, if it was a
specific sin, then it would likely have been accompanied by the definite article. But, you are entitled to your opinion in the matter. It should be apparent, however, that you are drawing from other parts of Scripture to "label" John's rather imprecise language.
I'm curious, since you've said that we are going to see a lot of THIS SIN, and according to your interpretation we have no obligation to pray for for such people--Are we to expect much prayer for persecutors, snitches, and hypocrites in the future?
Getting back to the text, even if there was a definite article, since there is no specific referent, the
definite term (could still refer somewhat vaguely to a class of sin. Furthermore, "sin" singular refers both to one act, and to rebellion against God generally. Some translations even render vv16-17 in exactly that way.
As it is, there is no article, so it is "a" sin (or simply "sin") leading to death, without specifying
what (single) or
which (of a class) sin John has in mind.
And with all due respect, what I've offered isn't a "meaningless" interpretation. You might not agree, and believe you have the better one. But that's not an analysis of my presentation that exposes its "inanity".
If you look at the context, John issues a very potent promise, vv14-15,
And this is the confidence that we have in him, that, if we ask any thing according to his will, he heareth us: And if we know that he hear us, whatsoever we ask, we know that we have the petitions that we desired of him.
John is writing to regular believers, some Christians for a long time, others mere children. I can imagine a young believer, especially, perhaps drawing the wrong conclusion to John's statements here, can't you?
"Anything? Whatever I ask? My son died, and he wasn't a Christian then, but he's probalby a lot clearer on the state of his soul right about now..."
John gives us, following v16, a very serious instance for prayer--praying to deliver someone from sin (general term)--which doesn't bring on death. And he says don't pray for someone (it's not any sort of option he gives) who has sinned himself to death.
Which makes perfect sense, given the mistake someone might make based on the earlier blanket statements. "Sure Joe might be dead, but God will certainly hear and seriously bring my prayer to bear on Joe's situation, because God's promise is to give us the GOOD things we ask for."
No, Joe is past the point where prayer will change anything in his regard. We KNOW that, because he's dead.
Bob seems to be abandoning the faith. He has really taken up with evil practice. He has been excommunicated. Bob's Mom is a Christian. Should we be telling her to quit praying for her son? After all, it's pretty obvious, right? he can't come back to Christ. That is a wrong assumption by my interpretation of this text. Bob's not dead yet, so let's keep praying for his redemption.
If this is a meaningless interpretation, I have to say it's pretty encouraging for being nonsense.