There is only one God'. What are some logics which can be evidence for this assertion?

I the Vedic version it is explained there are many gods, or demigods, as they are called, but only one supreme Lord.

Naturally there can be only one Supreme Person. If there were other supreme persons, none of them would be supreme. There can only be one Supreme God. It’s as simple as that. There may be different conceptions of the same God, but there is, logically, only one God.

Now the next question that comes up - which religion offers the best and most well documented version of God? Which religion can actually tell you who God is? Again, logic and reason tells us that the original religion on the planet, the most complete religion, the most ancient religion from God Himself, is the Vedic religion.

Note, I’m not offering an opinion here, I’m merely stating a fact.

Krishna says:

Now hear, O son of Prtha, how by practicing yoga in full consciousness of Me, with mind attached to Me, you can know Me in full, free from doubt.

I shall now declare unto you in full this knowledge, both phenomenal and numinous. This being known, nothing further shall remain for you to know.

Out of many thousands among men, one may endeavor for perfection, and of those who have achieved perfection, hardly one knows Me in truth.

Earth, water, fire, air, ether, mind, intelligence and false ego -- all together these eight constitute My separated material energies.

Besides these, O mighty-armed Arjuna, there is another, superior energy of Mine, which comprises the living entities who are exploiting the resources of this material, inferior nature.

All created beings have their source in these two natures. Of all that is material and all that is spiritual in this world, know for certain that I am both the origin and the dissolution.

O conqueror of wealth, there is no truth superior to Me. Everything rests upon Me, as pearls are strung on a thread. --Bhagavad Gita 7.1-7

Then Krishna says:

There are two classes of beings, the fallible and the infallible. In the material world every living entity is fallible, and in the spiritual world every living entity is called infallible.

Besides these two, there is the greatest living personality, the Supreme Soul, the imperishable Lord Himself, who has entered the three worlds and is maintaining them.

Because I am transcendental, beyond both the fallible and the infallible, and because I am the greatest, I am celebrated both in the world and in the Vedas as that Supreme Person.

Whoever knows Me as the Supreme Personality of Godhead, without doubting, is the knower of everything. He therefore engages himself in full devotional service to Me, O son of Bharata.

—Bhagavad-gita 15.16-19