I don’t think God needs another outside force, God has everything all in one. If motherhood implies something untrue about God in his relation to creation, then so would fatherhood, because one can’t be a father without a mother, unless we are restricting these terms to humans only.
I agree that God has everything all in One -characteristics of motherhood and fatherhood, but that’s the point. It’s all in One, whereas with humans it takes two. So do we call that One, Father or Mother? It can’t be both or that would be to project the duality of human parenthood onto God who is One.
I think it’s good to meditate on what motherhood reveals about God’s inner life but that doesn’t mean we can consider God as Mother. Motherhood DOES imply something untrue about God in relation to us but that doesn’t mean that everything about motherhood is untrue as far as showing us some characteristics of God. A human mother receives that which is outside of herself in order to be mother. There may be some kind of characteristic of God WITHIN His inner life of the members of the Trinity in their eternal exchange of love that motherhood reveals something about, but we are still talking about something that happens in God’s inner life, not something in relation to us. We can’t extract out some action of that inner life and call that Mother. Whatever that action might be, it is still in the context of the whole One, Undivided God who created us. It will probably always be a mystery.
Here’s a quote by Christopher West in which we can see that there are some characteristics of God that human love between male and female reveal to us but that is all WITHIN God’s inner life among the Three Persons and does not show His being Mother in relation to His creation.
“A ‘common union’ (communion) of persons is established to the degree that persons mutually give themselves to one another in sacrificial love… The Father eternally ‘begets’ the Son by giving himself to and for the Son. In turn, the Son (the ‘beloved of the Father’) eternally receives the love of the Father and eternally gives himself back to the Father. This ever-shared, ever-spirating love is the Holy Spirit who, as we say in the Nicene Creed,’proceeds’ from the Father and the Son.’ ….Perfect love–perfectly and eternally given, perfectly and eternally received, perfectly and eternally returned -that’s God.”
So if we have to choose whether to call God Father or Mother because He is One and not two, we can see that Father is correct in relation to His creation. He transcends humanity, is distinct from humanity, and is the origin of humanity.
Lastly, we must be obedient to Christ who told us to call God, Our Father, who is also His Father.