Verily in the beginning this was Brahman, that Brahman knew (its) Self only, saying, 'I am Brahman.' From it all this sprang. Thus, whatever Deva was awakened (so as to know Brahman), he indeed became that (Brahman); and the same with Rishis and men. The Rishi Vamadeva saw and understood it, singing, 'I was Manu (moon), I was the sun.' Therefore now also he who thus knows that he is Brahman, becomes all this, and even the Devas cannot prevent it, for he himself is their Self. Now if a man worships another deity, thinking the deity is one and he another, he does not know. He is like a beast for the Devas. For verily, as many beasts nourish a man, thus does every man nourish the Devas. If only one beast is taken away, it is not pleasant; how much more when many are taken! Therefore it is not pleasant to the Devas that men should know this.

In plain words: In the beginning Brahman knew only itself, saying "I am Brahman," and everything came from that. Any god, sage or person who wakes up to this becomes Brahman too. The sage Vamadeva realized it and sang, "I was Manu, I was the sun." A person who worships a god as separate from himself does not truly understand. The gods even prefer that people do not learn this, because people serve them like farm animals serve a man.