Gapon did not like the way that the people with little money were treated and so he decided to go to the castle and revolt.
When they went to the castle, their intentions were peace and they only wanted the king to sign a new deal.
Although they went in peace, the soldiers didn't believe so, and when the call was made, they decided to kill and injure a lot of them.
Many died and even more got injured and when the Tsar was informed of this incident, he was fuming. This shows that the Tsar wasn't a bad person, he really did want to help, however, he was a bad leader.