Once upon a time the gods won a great victory over the demons and they became arrogant. They boasted, “This victory is ours! This triumph is ours.” They failed to realize that the victory was won for them by the Brahman, with whose power the universe is created and in whom, at the end of the kalpa (aeon), it dissolves. The Brahman noticed the arrogance of the gods and appeared before them in the form of an Yaksha, but the gods failed to comprehend the identity of this wondrous entity.
They deputed Agni (the fire god) to ascertain the identity of the Yaksha. Agni proclaimed that he had the power to burn down the entire universe—the Yaksha asked him to burn a straw. Agni tried but he failed to set the straw ablaze. Then the gods deputed Vayu (the wind god) to ascertain the identity of the Yaksha. Vayu proclaimed that he had the power to blow away the universe. The Yaksha asked him to blow a straw. Vayu tried but he failed to move the straw.
After that Indra (the lord of the gods) was sent to investigate—the Yaksha presented before Indra a beautiful woman called Uma Haimavati. Indra asked her what this wondrous Yaksha was that had the power of hindering Agni from burning and Vayu from blowing. Uma Haimavati, who is the personification of wisdom, said, “This Yaksha is the Brahman. The gods are feeling pride over a victory that was won for them by the Brahman, so he has appeared as an Yaksha to teach the gods the lesson of humility.”
Since the gods derive their power from the One, the Brahman, they must not become arrogant. This story, which I have retold in my own words, occurs in the Book Three and Book Four of the Kena Upaniṣad and can be seen from two angles: first, it’s a moral injunction that the entities in positions of power must avoid arrogance; second, it’s an evidence of the monistic metaphysics of the Vedic thinkers.