You’re on very thorny ground here. There must have been hundreds of thousands of pages written about this (as jeidsath’s post intimates).
But for what it’s worth, I would take all three οτι’s as meaning something like “because.”
Other points arising from your translation:
ὁ ὀπίσω μου ἐρχόμενος ἔμπροσθέν μου γέγονεν, ὅτι πρῶτός μου ἦν. The subject is ὁ ὀπίσω μου ἐρχόμενος, article + participle: “the one coming behind me,” “he who comes after me.”
ἔμπροσθέν μου γέγονεν “has come into being in front of (or before) me”—liable to various theological interpretations, but expressed as a paradox.
ὅτι πρῶτός μου ἦν “because (or in that) he was ahead of me” (but the use of πρωτος, “first,” with gen. of comparison, is not entirely normal)—intended as a clarification?
The main thrust of the quoted words are clear enough, but there’s a degree of multivalence to them.
The quotation (the Baptist’s words) apparently ends there. It must be the evangelist himself beyond that point, as jeidsath says. But NT scholars already in antiquity disagreed about how far the “quotation” extended. *
The following οτι looks (to me) as if it’s elliptical: “(I mention JB’s prophecy) because …” It’s a common use of οτι, grammatically very loose. The entire passage is not very coherent; interpreters try to impose at least a semblance of coherence upon it.
In the last sentence, εἰς τὸν κόλπον τοῦ πατρὸς will go not with ἐξηγήσατο but with ὁ ὢν (again art.+pple like ὁ … ἐρχόμενος above): “the one who is in his (or the) father’s lap.” (In this period εἰς is often used where earlier and more literary Greek would use ἐν.)
But I think you’re right to find the sentence “a little weird and difficult to translate.” μονογενὴς θεὸς is a theologically fraught phrase, and there are textual variants in the manuscript tradition. Some have ὁ μον. θ. (making it rather the ὁ ὤν phrase the subject), some have ὁ μον. υἱός; these variants appear to be attempts to make the phrase simpler and more precise than it is.
εκεινος picks all this up: “he explained.” Just what he explained is not specified, but bible expositors like to try to pin it down (God whom no-one has ever seen?, the import of 16-17?, etc. etc.)—which seems to me a perfectly futile exercise.
Hope this helps!
PS There are no end of commentaries, none I would recommend, for reasons I’ve hinted at.
Edit. On the Greek of the NT generally, I’d advise you to steer clear of works on NT Greek, which tend to lump it all together and behave as if “NT Greek” were a unitary entity, whereas in fact of course there’s John’s Greek, Paul’s Greek, Apocalypse Greek, etc etc. You’d do better with treatments more conscious of the wider context of koine Greek. There are competing Companions to the Ancient Greek Language from Blackwell and Wiley, with separate authoritative chapters on different aspects or periods, there’s Horrocks’ “Greek,” recently revised, which pays due attention to Koine, and more. I’m failing to come up with the name of one particular essay that I’d recommend if I could only remember what it was.
For John’s in particular, I don’t know. I’ve seen some daft things said about it, but I’m sure there are good things too.
- οτι or no οτι, it seems quite clear that JB’s words don’t extend beyond v.15. But what is clear to the ordinary reader was not enough for early Christian and paraChristian theologians. Origen took the “quotation” to extend all the way to the end of verse 18, in opposition to Heracleon who took them down to the end of 17. Heracleon wrote an extremely detailed commentary on some of the John gospel, and his interpretations would seem utterly bizarre to Christians today (though his exegetical procedures are still practised). It’s fascinating to see how the gospels were interpreted before orthodoxy established itself.