Act IV scene 4 is crucial in building up a picture of Hamlet as he is forced to leave to go to England having killed Plonius and offended Claudius. As he leaves, he meets the Norwegian army that is going to fight over some "scrap" of Polish territory. Hamlet compares the willingness of soldiers in this army to go and die for something that must mean so little to them and to act on an issue that has so little personal connection to them. Fortinbras, who is fighting over this land, is an example of somebody who is willing to act and respond when he has reason. This of course is the direct opposite of Hamlet, who has significant reason for action but who has failed to act because of his procrastination. Note what Hamlet says in his soliloquy at the end of this scene about this comparison:
How stand I then,That have a father killed, a mother stained,Excitements of my reason and my blood,And let all sleep—while, to my shame, I seeThe imminent death of twenty thousand men,That for a fantasy and trick of fameGo to their graves like beds, fight for a plotWhereon the numbers cannot try the cause,Which is not tomb enough and continentTo hide the slain?