Life is merely a temporary charm.
Be good to all and do no harm.
Guru Nanak Dev ji reached Sialkot, now in Pakistan, on one of the Udasis (preaching missions). The people, who came to see him, told him that they were greatly worried about themselves and their city. Guru ji asked the reason for that. They said that a Muslim mystic named Hamza Gaus had gone on a 40 days meditation to destroy the city and its residents. This was because he was angry at the behaviour of one person. He made a decision to use his powers to make the whole city sink into the earth and make it vanish forever. Guru Nanak Dev assured them that no harm would come to them. They should go and get busy with their jobs and always keep God in their mind.
The Guru went to the place where the Pir had locked himself in a chamber in which he sat meditating to destroy the city. Bhai Mardana was asked to play on the rebeck while the Guru started singing a shabad. The Pir heard the music and virtues of God sung outside his chamber. He was so tempted by the celestial music/shabads that he broke his 40 day continuous meditation, opened the door and came out. He was surprised to see the Guru and his associates. He asked them, "Who are you"? Why have you come here and interrupted my meditation?"
The Guru told him to calm down and reminded him that holy men are expected to serve and help the people with the power and virtues God bestows on them. It is sin to use the holy powers to harm people. Pir insisted that all the people of the city were evil. None possessed any goodness. They all deserved to be destroyed. The Guru decided to reveal the truth to him. He gave some money to his associate and sent him to the city to purchase a packet each of "truth" and "falsehood."
The person went to the city and moved from shop to shop in search of truth and falsehood. He always got a negative answer to his query. Finally, he contacted Bhai Moola. He took the money and wrote on a piece of paper, Marna Sach, Jeona Jhuth. "Death is a truth and life is a falsehood."
The Guru showed this to the Pir and warned him that he was totally wrong to think of doing any harm to such people. There were people who knew and understood that life is temporary, hence, a falsehood. Death is sure to come to everyone. While after death, our soul lives forever hence, death is a truth.
Pir confessed that he was wrong to believe that everybody was bad and needed to be destroyed. He decided to serve the people and not harm them with the knowledge and virtues that God had given him.
Powers given by God should be used to help people and not harm them. Life is a temporary phase, death is inevitable.