Violence is mainly caused when the Jiv (creature) comes under the influence of one of the 5 vices – Lobh (greed), Kaam (lust), Krodh (anger), Moh (worldly attachment) and Ahankaar (pride). If one’s pride is hurt, it leads one to become angry and use violence against the person who may have instigated the hurt to one’s pride. Greed of money can lead one to use violence to attain worldly wealth. If one is blinded by Moh, one may get violent for the sake of false relations. Basically, violence is caused by these 5 vices and such violence is strictly prohibited in Gurmat.
Gurmat teaches us to be free of the 5 vices and not come under their influence. A Gursikh who indulges in chanting Gurmat Naam and obeying other teachings of Guru Sahib, is protected from the five vices and naturally stays non-violent. Gurmat teaches us to not fight or use violence to satisfy one’s selfish needs.
A Gursikh has so much compassion and is so non-violent that he can’t even pluck a flower for no reason (let alone hurting other Jivs).