In satyayuga there existed a demon called Kaalkepa. Kaalkepa was protected and supported by another demon Vritasura, but who was invisible to all except Kaalkepa. Together with the unseen Vritasura, Kaalkeya attacked the kingdom of the gods, Indraloka. King Indra and all the Devas went to Lord Brahma in desperation asking him the means to defeat the demon Kaalkeya, and his invisible friend Vritasura, who were torturing them.
Lord Brahma, told them that a weapon made of the bones of Rishi Dadhichi would kill Kaalkeya [and his hidden ally Vritsura]. He revealed further that a thousand years ago the Rishi had drunk molten iron and made his bones indestructible. The weapon made of the bones would kill the demons.
Taking Brahma’s advice, Indra with his army of Devas went to Rishi Dadhichi’s ashram on the banks of the river Saraswati, and worshipped him. Rishi Dadhichi, whose effulgence was like the sun, asked them what they wanted and as per Lord Brahma’s instruction, they requested him to give them his bones to defeat the deadly combination of Kaalkeya and Vritasura. The rishi gladly complied and shed his body effortlessly, just like a man removes his clothes. The Devas then took the bones from the rishi’s lifeless body and took it the divine architect Vishwakarma who made a hexagonal weapon out of them, called Vajra.
Meanwhile, Vritasura was waiting for Indra in the space between heaven and earth. He was surrounded by the Kaalkeya demons. A terrible battle was fought between the Devas and the Kaalkeya demons. The demons were winning the war and the Devas had begun to flee the battlefield. Desperately, Indra, as their king, went to Lord Vishnu for help. Lord Vishnu filled Indra with his luster, which made Indra very powerful. Seeing Indra grow so powerful, Vritasura started roaring loudly. The sound made the earth, the mountains and all the directions tremble and quiver in fear. Indra also started trembling, and accidently let loose the Vajra, and ran off to hide in a lake. The weapon went and pierced the demon Vritasura, killing him on the spot. With Vritasura dead, the Devas were easily able to defeat all the Kaalkeya demons. They found Indra, gave him the news that they had won the battle and told him he could come out of the lake.
On a deeper level, Vritasura represents our inner darkness. Vrit means to choose and Asura implies darkness. When there is no light of consciousness in us, we cannot choose rightly. Kaalkepa, which means the time factor, supports Vritasura, the hidden darkness in us. The demons of inner darkness and time can be killed with the luster of Vishnu and the weapon Vajra made of the bones of Dadhichi. Dadh means to hold. The yogi acquires the power to ‘hold’ by working on his vajra nadi through a technique called Vajroli. To do this, he uses both the mudra and its psychic counterpart, corresponding to the weapon Vajra and the luster of Vishnu, in the story. Once he controls the vajra nadi, its inner effulgence sheds light on his inner darkness and frees the yogi from time. The yogi having annihilated the inner demon Vritasura acquires the power to choose and consequently fulfill his wishes.