In plain words
In this way they came to believe that there is some power, and that this very power is God. Little by little they tried to learn numbers, as far as they could. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Among these ten numbers, one alone is the chief; all the rest are only different forms of it. If there is a number called two, it became two only because two ones came together. If there is a figure called nine, it comes about because nine ones are joined in it. All the other numbers are only changed forms of one. That is the truth they recognised. So it is One alone that is, as the chief. Ekaṃ sat viprā bahudhā vadanti. Though what is, is One alone, people go on taking it to be many numbers. That is the truth they went on recognising. In the Veda this very thing is ekoʼhaṃ bahu syām: what is, is One alone, and it goes on turning into many lakhs and millions. Without the one, it could never become two, or ten, or millions. So through these numbers human beings came to the truth that God, too, is One alone. Human beings came to believe that in the world there is a power beyond us, and that this power is one and not two. That One alone takes many forms and, through many forms and names, pervades the world.
It was on the basis of this very truth that it went on saying, Īśāvāsyam idaṃ jagat. The people of that age went on calling Him Ādityaḥ. Ādityaḥ means that Āditya is one of the twelve Ādityas, and that He is Viṣṇu. Viṣṇuḥ does not mean merely one who bears the conch, the discus, the mace and the lotus. Viṣṇuḥ is the principle that pervades everything. To such a Viṣṇu-hood we went on imagining a form. In truth, Viṣṇu-hood means all-pervasiveness itself. In what way did we come to believe the sun to be one? There are silver vessels, gold vessels, brass vessels, copper vessels and clay vessels of every kind; when all of them are filled with water, the sun is reflected in every one of them. The vessels are different and the vessels' values are different, but the sun is reflected equally in them all. Though thousands of vessels are set out, the sun is seen as thousands of suns. The vessels run into thousands, yet the suns become thousands. The sun is one alone. That is the truth they came to understand. The values, forms and names of these vessels may differ. Taking this as their basis, they came to believe that bodies are the vessels.