I'm only responsible for what I say, not for what you understand. Although as an author I am responsible for making readers understand--a reader who doesn't understand is an unhappy reader. (And there is some value to leaving some questions unanswered.
This quote shows how Prince Hamlet feels towards his uncle after the ghost Old Hamlet tells him that it was his brother that poisoned him and caused his death. Prince Hamlet promised his father that he will avenge his death.