This is something of a mystery, and we already discussed this in relation to elohim in Gen 1:1, but there is another aspect that is worth exploring further: the phrase here, “one of us” (כְּאַחַ֣ד מִמֶּ֔נּוּ, ka’echad mimmenu), does explicitly suggest one individual among a number. The expression is harder to explain as an emphatic plural—but still, perhaps, possible, because perhaps in the context of the emphatic plural elohim, the Hebrew for “as me,” instead of “as one of us,” would sound awkward. Another possibility is that God is addressing what is called the divine council, including the angels, seraphim, and cherubim; the fact that the cherubim make an appearance in the very next sentence makes this plausible. What is absolutely not likely is that God is addressing other actual divinities, because the same author of this text strongly inveighs against the notion of any other spirits being called “gods” at all. And of course, it is entirely possible that, before the author was familiar with the three persons of the Trinity, he was nevertheless inspired by the Holy Spirit to use the plural, communicating primarily with those who would come after.