Here’s a rather abstract question – why can one God be uncaused but two gods must be contingent? I think I have a hunch for an answer but it strikes me as very Eleatic.
God by definition is the origin of being or existence. The supreme being, first cause, God, is perfect and complete and therefore non-contingent.
The reason why two gods must be contingent is that both gods would be dependent on each other in order to complete the fullness of being. Each god would lack something – some perfection would be lacking. Thus, in order to complete the fulness of being and perfection, both gods would be needed together, and thus separately, they would be contingent on each other. God, by definition, is the necessary being. If two gods were required to make up the one necessary being, then both would be contingent (neither alone would be sufficient).
Since God, by definition is not limited and is not lacking in any being (and is the source of existence itself), then there cannot be two gods because both would be limited.
As far as the hierarchy of values, that is a problem also because if they were both perfectly identical in every aspect, then the qualities of one would be unnecessary since they are found perfectly in the other. If they were not perfectly identical, one would have greater powers than the other.
Every parent recognizes that one child has more experience than the other, is taller, weighs more and is thus different.
God possesses the fullness of knowledge – in the same way, if there were two gods, both would possess only partial knowledge (since one could not know what it is to be the other).
There are many other problems. With two gods, each is lacking something. That lack is an unfulfilled potential. But there can be nothing unfulfilled in the nature of God.