Guruvaar Vrat is observed on Thursdays to honour Brishaspathi Deva and get his blessings. Once Lord Indra lost in his indulgences did not pay respect to Brishaspati Deva when he visited his court. To which Brihaspati who was the Guru of Indra felt bad and walked away. Then Indra realised his mistake and decided to seek his Guru’s forgiveness and went towards his ashram.
Guru was quick to realise Indra’s intentions and disappeared from his ashram to teach him a lesson. When Indra could not find Guru, he returned back disappointed. The mighty demon Vrishvarsha saw this as an opportunity and sought his guru Shukracharya’s blessings to attack Indra. Then he attacked Swargaloka with his full strength and Indra lost all the battles without the guidance of his Guru.
Then Indra and the Celestials went to Brahma and related the whole story. Brahma adviced them to seek the blessings of Vishwaroopa who was the son of demon Tvashta and get him as the priest and perform yagna. Then Vishwaroopa performed the yagna and Indra was able to defeat the demons and regain his empire.
Then Indra was pleased with the results and decided to perform a special yagna for further gains and asked Vishwaroopa to perform the same. Vishwaroopa had three mouths and he used to drink soma rasa from one of his mouths and eat meals in the other one.
The demons then tricked Vishwaroopa and asked him to perform the Yagna for the benefits of demons as well as he also came from the same background. Then Vishwaroopa performed the yagna and the benefits were divided among the gods and demons.
When Indra came to know about this, he beheaded Vishwaroopa in a fit of anger. Then Indra had to face the consequence of killing a brahman and his body turned sacrilege. Again all the gods approached Brahma and sought the remedy for this problem. Then Brahma along with Brishaspati decided to divide the sacrilege into four parts and distribute it among earth.
Thus deserts took some part of the sin and water took some part of the sin and trees took some part of the sin and the entire womanhood took some part of the sin as signs of menstruation every month.
It is believed that when one listens to this Katha during Guruvaar Vrat, he would be free from sins.