I had already written a lot on 1 John 2:2; which as I noted up front was the most difficult of the passages to comment on for various reasons, not least because it’s the verse that looks most, at first glance, like it runs at least somewhat against the thrust of the other verses. So I didn’t add in a discussion of specific translation issues, even though those are important, too; figuring that someone would ask about them eventually anyway–thus giving me an excuse to ramble on at even greater length on the topic. {g}
So, first things first.
The UBS/Nestle-Aland Greek text (with my usual underscores after long ‘o’ and long ‘e’):
kai autos hilasmos estin peri to_n hamartio_n he_mo_n ou peri to_n he_metero_n de monon alla kai peri holou tou kosmou
The text is settled across all copies, with no significant variations to mention (even by the broad standards of the UBS as to what might even remotely count as a significant variant.) So that won’t be a problem.
Comparing a few translations I have at hand which trend more literally than usual:
Knoch’s Concordant Literal: “And He is (the) propitiatory (shelter) concerned (with) our (the) sins, yet not concerned (with) (the) ours only, but concerned (with) (the) whole world also.”
Green’s Textus Receptus 3rd Edition, literal: “And He is (the) propitiation relating to our sins, and not relating to ours only, but also relating to all the world.”
Green’s TR 3rd Edition, super-literal: “and He a propitiation is concerning the sins of us; not concerning ours but only, but also concerning all the world.”
(Incidentally, Green prints {esti} instead of {estin} as the chief verb of the first clause; I’m not sure if that’s a printer oversite, or a variation of the TR’s sources which he thought was significant to include instead. Anyone wishing to volunteer a significance in the difference of the be-verb there–which there might be–certainly has my blessing to try! 
The TR is identical here to the USB’s critical compilation otherwise; probably because, as noted, there are no significant variations in the record.)
{kai autos} – “[conjunction] He”. {Kai} is a multi-purpose conjunction connecting sentences or clauses, but stronger than {de} which serves much the same functions. There are no signs of this being one of the weirder uses of {kai}, so it probably means “and”, “but”, or “yet”. In hindsight, context established afterward in the sentence eliminates “but” or “yet” from liklihood, leaving over “and” which is the most popular meaning for the word anyway. “He”, as noted earlier in my analysis, is virtually certain to refer back to Jesus Christ the Just, from the end of the previous sentence.
{hilasmos estin} – {estin} is a third person singular is-verb, matching back up with {autos}. {hilasmos} is thus most likely a predicate noun which we would put on the other side of the verb in English (but which is probably being fronted here for relative emphasis): “And He is hilasmos”. {hilasmos} is an unusual form of {hilas-} in the New Testament texts; which, as previously noted, only appears here and a little later in 1 John’s fourth chapter where the surrounding clause is essentially repeated. The word is certainly being used as a noun, though it isn’t the word’s normal noun form in the NT which was used in the Greek OT (and afterward) as a nickname for the throne of God in judgment emphasizing the joy of His mercy. Consequently, though Knoch translates it “propitiatory shelter” (like the hilastarion itself), I thought it would be more in keeping with the simpler noun form to leave it as “propitiation” (like Green and most everyone else, incidentally).
There is no definite article for this noun; but one might or might not be intended anyway (this being Greek), and since it seems a pretty important noun I was inclined to supply a “the”. But I nodded in the direction of providing more options (since the actual language allows it), so I went with “a” instead (as we would literally translate in English) and optioned “the” parenthetically. No article at all might also work: “And He is propitiation”. If someone wants to try that, I have no immediate objection.
There are no other words for this clause. It is complete: {kai autos hilasmos estin}. (Or maybe {esti}, per Green’s TR?? As I said previously, I would be curious to see some discussion on that, although I suspect it’s only a printer’s glitch, since Green doesn’t apply the verb translation any differently than anyone else I’ve ever seen.)
{peri} – This is simply the preposition “about”. There isn’t anything else around it that would feasibly modify it into anything else, so that’s how I left it. Obviously it sounds a little weird in English, so there are various attempts at paraphrasing; but to be accurate, they ought to keep the notion of “about”. “Relating to” is pretty good; “concerning” or “concerned with” isn’t bad. (That’s Green and Knoch, respectively, though Green has both “relating to” and “concerning”.) “For” is quite wrong, though. (My NASV, which may be somewhat out of date now, has “and He Himself is the propitiation for our sins”; so does Vine’s Expository Dictionary for their entry on {hilasmos}–ironically calling down the King James’ Version for adducing “of their sins” in parenthesis later in this verse, by the way. 
They’re correct about that; wrong about the “for”. My Holman Christian Standard has “for”, too. Somewhat amusingly, when I looked up {peri} in Vine’s index at the back, “for” wasn’t one of the translation options; rather two synonyms for “about”, and also “of”. Interestingly, not simply “about”; I’m not sure why, since {peri} is one of the first prepositions any Greek student learns.)
The preposition “about” implies an expected object of the preposition, and sure enough that’s what comes next.
{to_n hamartio_n he_mo_n} – literally “the sins us”, but with special suffix modifications to the possessive. So literally “the sins of us”; or “our sins”. (“The sins” is modified in their suffixes, too, in order to connect grammatically with {he_mo_n}’s possessive sense.)
So the full phrase here is {peri to_n hamartio_n he_mo_n}: “about the sins of us”, or “about our sins”.
{ou} – literally “not”; which can be used several ways, but also like our contrasting English conjunctive usage of “not”. Which, in contextual hindsight, is what’s happening here. (If you’re wondering why I translated an “and” in front of it, don’t worry, I’ll be getting to that soon.)
{peri to_n he_metero_n} – {peri} is simply “about” again (though the guys who translate it “for” previously tend to keep translating it that way instead, which would probably be right, on the principle of consistency in parallel usage, if “for” was the correct preposition to begin with.) {to_n he_metero_n} is the object of {peri}’s preposition; and like before the term is itself a couched prepositional possessive phrase. In this case, it literally means “the ours”, but we wouldn’t normally use a direct article there in English (that happens a lot in Greek) so it’s understandably omitted in translation. I could have gone with something like “about these of ours” or “those of ours” though.
{de monon} – {de} is a weak multi-purpose conjunction (like {kai} but not as strong). It’s a little weird to find it here in the sentence, because usually it would be signifying the beginning of another sentence or clause. But {monon alla}, for reasons I’ll get to in a minute, can’t be a new clause or sentence being begun by {de}. The way Greek works, however (which can be deeply irritating at time 
), words like this can be kicked back in the sentence when the author wants to emphasize other words for whatever reason; and that’s what’s happening here: {de} has been “postpositived” into the backfield. In English, we’d put it up near the “not”; so it could mean “and not” or “now not” (unlikely, though “now, not” might work with a nice pause for emphasis) or “yet not” or even “but not” (though usually something stronger is used for “but” than {de}.) Considering the way the rest of the sentence ended up translating out, I went with “and”, but “yet” would work okay contextually, too. (However there’s an important “but” coming up soon, so I didn’t want a weaker “but” like a “yet” in the foreground; “and” sounded smoother.) {monon} means “only” or “alone”. It could be put at the end of the whole phrase in English (for example “and not about ours alone”), but I wanted to emphasize it more and it sounds smoother (to my ear anyway) as an adverb to “not”; thus “not only”. I wouldn’t qualm putting it back toward the end, though (as all the translations I immediately have at hand prefer to do, by the way.)
{alla kai} – {alla} is the strongest way in Greek to say “but”; and when it’s followed by {kai}, especially with a recent {ou} and {monon} in the previous phrase, then we’re looking at one of those weird uses of {kai} as something other than a normal moderately strong conjunction: “but also”. So this second part of verse 2 is a “not only this but also that” comparison.
{peri holou tou kosmou} – “about” (duh); and the object of its preposition is not itself a prepositional phrase this time, possessive or otherwise. It’s only {holou tou kosmou}. {tou kosmou} is {ho kosmos} suffixed around to fit grammatically with {peri} (which in this case changes the “the” to another form): “about the cosmos”, or “universe” or “world” or “creation” (in the sense of artistic decoration; which for those who don’t know is why people who work on decorating the hair, face and hands etc. are called “cosmetologists”. It’s also where we get the word “cosmetic” from and some other terms of that sort referring to decoration. The Greeks applied that term as a flattering description of all reality, sometimes in the sense of being a real design of the gods or whatever, and sometimes in the sense modern atheists still like to talk of “design” in Nature, even though they don’t really mean “design”.) {holou}, meanwhile, is our English adjective “whole” without twenty centuries of spelling tweaks but with a local grammatic suffix.
Thus my (previously unstated) rationale for the translation: “And He is a (or the) propitiation about our sins; and not only about ours, but about the whole world, too.” I could have used “also” up after “but”, instead of “too” at the end; or an “as well” at the end instead. In hindsight, maybe I should have done it that way for a little more fidelity to the word order in Greek; but I thought this might help highlight that the term at the end (so far as I can tell) isn’t “the whole world’s” but “the whole world”–which might, to be fair (I mean to non-universalists), be significant in comparison. (The Vine’s editors certainly think so, for example.)
I didn’t think so. {shrug} 
I think I translated the sentence pretty faithfully.
Most of the translation is pretty straightforward; I don’t think there’s going to be a lot of variance between translations, except insofar as guesses about how to translate the unusual noun form of {hilas-} found here–which I thought I was pretty conservative about: all the other guys I’ve mentioned so far agree with “propitiation” except Knoch (whom, as the only avowed universalist of the bunch, you might have expected me to be ideologically preferential toward instead–though I’m not, for reasons I’ve now mentioned); and I even agree with them that “the” is intended before “propitiation” (though as a nod to people who might not agree I allowed “a” there instead and parenthesized my own preference).
The main sticking point is that I translate {peri} as “about”–which is what the word typically means–whereas a number of translators prefer “for” instead–which is not what the word typically means, and for which translation there isn’t any grounding in the surrounding context.
“but also about the whole world” may be unexpected, in that it doesn’t seem to parallel “not only about our sins”; but in fact that’s how the Greek reads. I think I end up treating it as though it reads “those (sins) of the whole world” or “the sins of the world world” anyway–which would annoy Vine’s and their Arminianistic application of the distinction. Nevertheless, the distinction is there, so I included it. I try to be fair that way.
You never bothered to mention why you thought the sentence was now nonsense, the way I translated it, by the way; and I need dinner now. So, since this comment is already way long, I’ll stop here for now and give you an opportunity to correct me on how the Greek should be translated instead and why–I’m far from being an expert at it, so I try to follow cues from people who know the language better.
I’ll get to your other remarks later, tomorrow I hope. Though relatedly:
A good thing I didn’t, then, hm! I think I was pretty consistent about how I did translate it (including in subsequent application), which was, “In this is love: not that we love God, but that He loves us and dispatches His Son a propitiation about our sins.”
You’re welcome to correct me on how the Greek should be translated there, too. Please be detailed. Also, if you quote me on how I translated it, try to actually quote me next time instead of importing something similar to another translation I did as though that’s how I translated this verse, too.
(Admittedly, I do think God sent His Son “to atone all into Him” (as Col 1:20 puts it)–“all” including “us”–but that is not at all how I translated this verse. I didn’t even apply my translation of this verse that way. I don’t mind if you criticise how I translated and applied translation for 1 John 4:10, but claiming I “mangled” a translation by quoting me as though I translated that verse a substantially different way than I actually did, is not helpful.)
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