Skanda Shasti festival like most other Hindu festivals celebrates the victory of good over evil. Skanda is also known as Lord Muruga, Subramanya, Kartikeaya and Kartik. Skanda Puranam narrates the origin of Kanda Sashti fasting.
According to Skanda Puranam, the longest of the 18 Mahapuranas, the demons under the leadership of Surapadma, Simhamukha and Tarakasura defeated the Devas and took over the earth. They found immense pleasure in torturing the Devas and humans. They went on a massive rampage and destroyed anything that belonged to Devas.
Surapadma had got the boon that only a son of Shiva will kill him. The demon had thought that Shiva who had gone into deep meditation after death of Goddess Sati will never return to earthly life.
Devas took refuge at the feet of Lord Shiva but Shiva was in deep meditation. On the advice of Lord Brahma, Devas took the help of Kamdev or Manmatha to incite sexual desire in Shiva. Kamdev succeeded in his mission but an angry Shiva burnt him into ashes.
The semen that got emanated from Shiva got divided into six parts and was deposited in the Ganga. Goddess Ganga deposited the six parts in a forest and it assumed the form of six children. The children were looked after by the six Karthikai stars. Later, Goddess Parvati combined the six babies into one. Therefore Lord Muruga is depicted differently sometimes with one face and two arms, sometimes with six faces and twelve arms and in some places with single face and four arms.
The demons continued their rampage and Soorapadman held son of Lord Indira and many other saints and devas as captives. Lord Subramanya soon adorned the role of general of Devas and decided to annihilate the demons. He soon defeated the demons.
In the final battle, Lord Muruga killed Soorapadman with his ‘Vel’ and this act of the Lord is known as Soorasamharam. The main Skanda Shasti festival is held on this day.
The famous ‘Vetri Vel’ chanting that takes place on the Shasti day is associated with the victory of Skanda over Soorapadman.