Lib here is something that you’ll just to take my post as my cite*: We do love our poetic metaphors and again Torah is chock full of 'em but God’s oneness is not a metaphor in Judaism; it is the central concept and the central prayer. It’s the closest we got to a creed and by some accounts is one.
*Ach, I could find dozens of supporting documents if you want, but honestly, just trust me on this.