The very essence and soul of everything in a comprehensive theology is the acknowledgment of God [arising] from a concept of him. Therefore it is necessary to begin with the oneness of God, and to prove it point by point:
1. The whole of Sacred Scripture teaches that there is one God, and therefore so do the theologies of the churches in the Christian world.
2. The recognition that God exists and that there is one God flows universally into human souls.
3. As a result, every nation in the whole world that possesses religion and sound reason acknowledges that God exists and that there is one God.
4. For various reasons, different nations and peoples have had and still have a diversity of opinions on the nature of that one God.
5. On the basis of many phenomena in the world, human reason is capable of perceiving and concluding, if it wants to, that God exists and that there is one God.
6. If there were not one God the universe could not have been created or maintained.
7. Those who do not acknowledge God are cut off from the church and damned.
8. Nothing about the church is integrated in people who acknowledge many gods rather than one.
These points will be explored one by one.
from True Christianity, Section 5