Act1 scene 5 what terrible responsibility does the ghost lay on hamlet?

In Act I scene 5 of Shakespeare's Hamlet, the ghost of Hamlet's father tells his son he must avenge his death at the hands of Claudius. Claudius is Hamlet's uncle who poisoned his own brother, Hamlets father, in order to steal his wife and his crown. Hamlet's father orders him not to harm his mother Gertrude but to let Heaven take care of her for her part in the matter.