Why is the Ghost "armed"?the question is in act 1
Two reasons that I have always considered are:
1) he is at war with his murderer. He must get across the young Hamlet the seriousness of the situation. Young Hamlet must commit to getting revenge for King Hamlet's untimely death.
2) the country really is at war. They are preparing the defend themselves against Fortinbras who believes that the land the Danes have rightfully belongs to him. In the end, he gets it anyway as Hamlet's dying breath is an edict that gives the throne of Denmark to Fortinbras.