There was a sikh called Bhai Mona who was serving in the langar of Guru Angad Dev Ji Maharaj. Mona was extremely arrogant and greedy. Some people complained to the Guru the insulting behavior Bhai Mona displayed whilst serving langar. The Guru called him for an explanation. Bhai Mona said that he was the servant of the Guru and would do anything for him and that he was not a servant of the others( sangat).
The Guru than asked him to go to the nearby forest, chop some wood, make a pyre and cremate himself. Without understanding the consequences of the Guru's orders he went to the forest, cut the wood, makes a pyre and lit it. On seeing the blazing fire he became scared and was reluctant to jump in the fire. Meanwhile a thief arrived and asked Bhai Mona what he was going to do. Bhai Mona told him the whole story. The thief (who was good at heart) thought that he had an opportunity of wiping out the sins of his past life. He accordingly said to Bhai Mona that he would give him a bag of jewels if he would let him die on the pyre and get salvation. Bhai Mona happily agreed.
The thief jumped in the fire but was saved by Guru ji's grace. Bhai Mona on the other hand was arrested for the theft of the jewels and was hanged.
On hearing this the Guru said that a sinner could get salvation by believing in and obeying Guru's orders no matter what he had done before; whereas the pride and vices like anger and greed would destroy the result of all the service(when done in ego).