The revelation of God in the Jewish Scriptures was “pregnant” with the later revelation of the Trinity. The Jews knew God as Creator of “the heavens and the earth” (i.e. everything), God was their Savior and Deliverer, and there are frequent references to the “spirit” of God.
Mystically, God is referred to three times in the greatest prayer commanded of the Jews (see Deut 6:4 and following):
Hear, O Israel, the LORD is God, the LORD alone.
The sacrifice of Isaac and the animal sacrifices in the Temple foreshadowed the ultimate sacrifice of the Son to the Father…
Read Romans Ch 11 on how God intentionally hid Himself from the Jews, even to this day, as part of his plan of Salvation. But, ultimately the revelation of God in Three Persons should delight the Jews, as being beyond their acknowledged faith of the ineffable God up to that time. There still is but One God, but that Godhead has been revealed in Christ as beyond the wildest imagination of the Jews. It’s a lesson for us all not to worship gods of our own making and thinking.
Read Salvation is from the Jews by Roy Shoeman.