Note: this page is a list of statements, not a single statement to give reasoning for. Reasoning on pages such as these are not to describe the reasoning behind each statement. Instead, they are to explain how all the above statements, if true, can be held in harmony and lack contradiction.
St. Augustine in Confessions
∴ only one God exists is compatible with the The Father is fully God, the Son has always been fully God, and the Spirit is fully God