Why There Must Be Duality within Humanity

Then the LORD God said, “It is not good that the man should be alone; I will make him a helper fit for him.” 
Genesis 2:18

The reason why the solitary existence of the man is not good is not because it forces the man to endure isolation and loneliness nor because he must face the challenges of life without human assistance--sentimental readings like these find little basis in the text--but because he has been endowed with the divine image and hence with the capacity to empty himself sacrificially into another.  Such an endowment cannot be enjoyed unless there is at least one other person.  For there to be an exchange of self-giving love, there must be duality within humanity.  As a lone human, Adam cannot manifest the divine image.

--Tim Savage, No Ordinary Marriage: Together for God's Glory, p.34-35 (emphasis added)

Biblical theology at its finest.