I must be cruel to be kind.”
This announcement does not seem to make sense. How can an individual treat others kindly even when he is cruel? However, Hamlet is talking about his mother, and how he intends to kill Claudius to avenge his father’s death.
This act of Hamlet will be a tragedy for his mother who is married to Claudius. Hamlet does not want his mother to be the beloved of his father’s murderer any longer, and so he thinks that the murder will be good for his mother.