God is one. The great emphasis of the First Testament (Old Testament) is the oneness of the only true God, the God of Israel (Dt 6:4, Isa 42:8, 43:10, 1Ki 18:39).
The common word “one” is ehad. It is seen over 900 times in the First Testament and it carries the idea of a composite unity. The same word is used in describing one flesh between one man and one woman as husband and wife. (Ge 2:24). A related word, yahid characterizes “solitary, alone,” but it is not used of God in the First Testament.
God speaks using the designation “we” and “us” (Ge 1:26, 3:22, 11:7, Isa 6:8); some relate this to angels or a divine council but only with difficulty. Elohim and Adonai are both in the plural form. They are almost always used with singular verbs and modifiers as proper names. Other plural terms for God are rarely translated (Ecc 12:1 lit. “Creators”).
“The First Testament and Intertestamental view of God was less individualistic than today. The Spirit of God (Ge 1:2), the Word of God (1:3; Ps 33:6), Wisdom of God (Pr 8:22-31), the Angel of God (Ex 3:2-15, and sometimes the Messiah (Isa 9:6; Mic 5:2) were seen as both God yet God as distinct from God. Isa 48:16, 44:6, Zec 12:10, Ps 45:6-7, 110:1. These apparent divine agents were personified and ascribed divine attributes.” — Dr. Horrell, DTS.