People who acknowledge one God in their belief and worship one God in their heart are in the communion of saints on earth and the communion of angels in the heavens. Each of these groups or communions is called a partnership, and is a partnership, because there is one God among its people, and they are in the one God. These same people also have a partnership with the entire angelic heaven. I would even go so far as to say they have a partnership with each and every one in heaven. For they are all like children and descendants of one parent, with such similar minds, mannerisms, and looks that they recognize each other as relatives. The angelic heaven is laid out in communities on the basis of all the varieties of love for what is good. All these kinds of love aim at one most universal love: love for God. All people who direct the acknowledgment of their faith and the worship of their heart to one God who is the Creator of the universe and also the Redeemer and the Regenerator are descended from that love.
Exactly the opposite is true of people who adore, and seek help from, many gods instead of one. The opposite is also true of those who say one God but think three. This is the practice of people in the church today who divide God into three persons and hail each person as a God in his own right, and who attribute different qualities or properties to each one that the others do not have. This leads to actual divisions not only in the unity of God but also in [Christian] theology itself, and even in the human mind in which that theology has to live. What other result could there be except confusion and discontinuity in the teachings of the church? In the appendix at the end of this work I will show that this is the state of the church today.
The truth is that dividing God or the divine essence into three persons, each of whom is individually a god in his own right, causes denial of God. It is like someone entering a church for worship and seeing a triptych above the altar with one god portrayed as the ancient of days, another god as a high priest, and a third god as Aeolus flying in the air, with an inscription reading, These Three Are One God. Or perhaps it is like the same person seeing a painting above the altar that portrays God’s unity and trinity as a deformed person with three heads protruding from one body or three bodies sharing a single head. If people enter heaven with this as their picture of God, they will definitely be thrown out headfirst, even if they plead that the head or heads stand for God’s essence and the body or bodies stand for God’s distinctly different properties.
from True Christianity, Volume 1, Section 15