Leartes and Fortinbras share the same fate as Hamlet, the three of them lost their fathers in unfortunate circumstances. They feel the same kind of grieve of losing a loved one. But each reacts, differently. Their behaviour play a close related trait towards advice and duty, action versus inaction and sanity versus madness. Hamlet and Leartes want to get revenge, while the first is looking forward is getting the throne back and considers the consequences of his actions. Leartes, on the other hand, is blinded by his feelings (madness) and takes belligerent actions without thinking on the consequences.
Hamlet and Fortinbras, want to take revenge both. Whereas Hamlet only seeks to get the throne back and keeps on devating on how and when to take action, Fortinbras wants to clean his family's name and fights in an orderly fashion, with the use of an army.
I would say it’s about using your life usefully. In other words, the summary is about “Making use of one’s life”.
Hope it helps!
For us to find out this question we would have to read the full book! Very sorry
