It is bordering on the banal to say that human beings have a tendency toward superficiality. Surface deep, with a great hollowness on the inside. The problem is that we try to hide our hollowness. And we do this in all kinds of ways. Education and learning is a great way to hide hollowness. Philosophically we can construct ontologies (theories about the nature of existence or being) that give us a solidity below the surface. Sartre was suspicious of these philosophical systems, which is why he coined the idea that existence precedes essence. (To prevent being defined before we live into ourselves.) Deconstructionists claim to have revealed the lie behind most of Western philosophy, showing the emptiness behind the great philosophies of being.
We can be tempted to mimic this 'fullness' with great theologies of substance in the attempt to fill up what is in fact the great hollowness at the heart of human existence. We need a theology that, instead of hiding our hollowness, allows us to live it.
We can begin this theology of hollowness with the Trinity. (Where else!) Trinitarian being (but remember God's 'being' when applied to God is not univocal; see the posts under 'transcendence') is not a fourth 'thing' next to the three persons of Father, Son and Spirit. Without the persons there is no divine substance left over. This provides a realness to personhood in the Trinity: the person is not a layer over some originate 'stuff'. Therefore when you encounter the persons you are encountering God, not a mask with God remaining a shadowy figure behind the mask. But this also leaves an emptiness or space at the very heart of God, because personhood is, in the Trinity, defined through relationship. God is eternally father, which means that God must always be defined through relationship with this other we name Son, and a relationship marked by utter self-giving and receiving, making space for the other to be the other, etc. We must think of the being of God in terms of this movement, and the identity of each person in terms of their relationship with the other. When we think of the Trinity like this we are taken away from a thick treacle-like understanding of being to a more dynamic understanding, an understanding that is a far cry from God being 'stuff'. This understanding of God is the justification for an anthropology that makes us less treacle-like beings, and more lithe with a hollowness waiting to be filled in a dynamic embrace of love. And that is the realm of Christology, specifically, the doctrine of the Incarnation.
