• The Laws of Logic Hold Universally
• Christianity's distinctive, characteristic beliefs

This has been flagged as an appeal to authority. Before removing this flag, ensure the reasoning is based on the evidence the authority had, not the authority itself.

• The ecumenical councils held the position that only one God exists.
• The positions of the ecumenical councils have stood up to scrutiny for 2,000 years.
• If the positions have stood up to scrutiny for 2,000 years, they are true.
• If the above is true, only one God exists

∴ only one God exists

x only one God exists