All the elements of human reason unite in, and in a sense center on, the fact that a single God is the Creator of the universe. As a result, rational people, on the basis of their shared understanding, neither do nor can think in any other way. Tell people of sound reason that there are two creators of the universe and you will feel within yourself how they recoil from this notion, perhaps simply from the tone of their voice in your ear. This enables us to see that all the elements of human reason unite and center on the oneness of God.
There are two reasons for this. The first is that in its own right, our very ability to think rationally is not our own property. It is a property of God within us. Human rationality in general depends on this fact, and this general property causes our reason more or less spontaneously to see the oneness of God. The second is that through our rational ability either we are in heaven’s light or we draw from it some general quality of its thought, and the all-pervading element of heaven’s light is that God is one.
This is not the case if we have used our rational ability to skew our lower understanding. In this case we still possess the ability, but by the distortion of our lower abilities we have steered it off course, and our rationality is not sound.
We may not be aware of it, but we all think of an aggregation of people as a single individual. So we understand right away when someone says that monarchs are the head and that their subjects are the body, or when someone says that this or that individual has some particular role in the body politic, that is, in the realm. It is the same with the spiritual body as with the civil. The spiritual body is the church, whose head is the Divine-Human One. We can see from this what kind of person a church would look like under this construct if we were to think not of one God as creator and sustainer of the universe but of many gods instead. We would apparently be envisioning a single body with many heads on it—not a human being, then, but a monster.
If we were to claim that these heads have a single essence that made them all one head, then the only possible image would be either of a single head with many faces or of many heads with one face. In our perception, then, the church would look grotesque. In fact, one God is the head, and the church is the body that acts at the bidding of the head and not on its own, as is true of us as well.
This is also why there is only one monarch per realm. More than one would pull it apart; one holds it together.
from Divine Love and Wisdom, Sections 23, 24