The Hebrew use of a plural “elohim” to mean God is the royal usage; kings and emperors commonly referred to themselves in plural. Similarly, “Let us make man in our own image” is interpreted to be either that same imperial “we” … or be a discussion between God and some heavenly beings (angels, etc.)
Pharoah does something similar in worrying about the Hebrew slaves, and no one suggests that he is a plural Pharoah.
I would not call two minor grammatical points “Plenty of OT for the plurality of God.” However, that argument has been used by Christian proselytizers to try to convert Jews who are ignorant of Hebrew.
The notion of a two gods – masculine and feminine – was obviously fairly early, usually representing sky and earth respectively, with fertility connotations (rain comes from sky to make earth fertile, etc.) [sarcasm] Do you suppose the Christian move to three gods was a sort of one-upsmanship?[/sarcasm]
As tomndebb says, the emergence of the notion of three-in-one was the effort to combine the notion of divinity of Jesus with the notion of monotheism.
As a side note, Jewish rabbinic thought said that one may break any commandment to save one’s life, except for three: idolatry, adultery, and murder. If the Nazi holds a gun to your head and says, “Kill that person,” one accepts martyrdom rather than commit murder. The rabbinic question at the time of forced conversions was whether Christianity would be viewed as “idolatry” on account of having three gods and lots of statuary. The initial rabbinic decision was that Christianity was indeed idolatry, and therefore Jews should accept torture and martyrdom rather than forced conversion to Christianity. Islam, on the other hand, with an insistence on a single god and absence of statues or pictures, was NOT idolatry, and one should accept forced conversion to Islam rather than death.
The Christian leadership protested strongly, of course, and the rabbinic ruling was later reversed. However, the Jewish (outside) perspective of Christianity is still somewhat dubious. [snide] If it looks, walks, talks and smells like three gods, what’s the difference if the clergy says it’s only one? [/snide]
OK, I’ll stop, other events this morning have me in a nasty mood, and I humbly crave pardon from my Christian friends.