Shumbha and Nishumbha were two Asura (evil forces) brothers who obtained a boon from Lord Brahma that they will not be killed by any male either human being or animal, as they felt there was no female strong enough to defeat them in battle. Thus empowered, these demons started disturbing the prayers of the saints torturing them and asking them to worship the duo rather than any other deity. The Gods realising that they cannot defeat the two brothers sought protection from the Goddess Parvati. Parvati created another Goddess from her own being who came to be known as "Kaushiki". As She was stunningly beautiful, when Chanda and Munda, the disciples of Shumbha and Nishumbha saw her they reported her beauty to their masters. Upon hearing this, the two brothers sent a marriage proposal to the Goddess. The Goddess told them that she had taken a vow to marry the one who can vanquish her in battle and take her forcibly. Thus incited into battle, Shumbha and Nishumbha first sent a large army which was promptly defeated. They then sent Chanda and Munda whom the Goddess defeated assuming the form of Maha Kali and thus She was also named 'Chamundi', the one who beheaded the Asuras Chanda and Munda.
As the battle became more fierce, seven more Goddesses or Shaktis emerged from the bodies of seven Gods to assist the Goddess in this battle. At that time the mighty demon Raktabija was also sent to battle. Raktabija had been granted the boon that wherever his blood fell on the ground it would take the form of a 'Bija' or seed and from it would sprout another Raktabija. To slay him the Goddess asked Kali to lick the blood of the Raktabija before it fell on the ground. The goddess in the meantime beheaded the demons. All the Shaktis then together killed Nishumbha and his army leaving just Shumbha. When Shumbha realised that he had been outnumbered, he taunted the Goddess that she alone cannot defeat him and needed the help of seven other Goddesses to do so. The Goddess merged all the Shaktis into herself and single-handedly killed Shumbha thus freeing the world of evil.
“Shumbha” means doubting oneself and “Nishumbha” means doubting others. Thus the combination of Shumbha and Nishumbha means doubting everything and doubting at every step. When the mind is congested with doubts about one self or others, there is no mental peace. Doubts thus drain the sustaining life force energy and prevent spiritual growth.
“Chanda” and “Munda” – Chanda means opposite head. Chanda will oppose anything you say. Chanda is one who cannot agree with anything. “Munda” does not have a head at all. He will not listen to reason. Therefore erroneous logic and perception prevail. The noose of light used by Devi represents wisdom. True knowledge is uplifting as it purifies the mind with unwavering clear logic.