Who was sleeping in the second chamber in Macbeth? Why did Shakespeare include that information in the play?
In Act II, who was sleeping in the second chamber next to King Duncan and why was that information important to the play?
That King Duncan's sons Malcolm and Donalbain are asleep in the chamber next to their father is important for several reasons. First, it gives the sons a plausible rationale for fleeing the country, Malcolm to England, Donalbain to Ireland. This will be important to the plot further on when Malcolm returns from England with an army to confront Macbeth. They also have good reason to run away, as they rightly fear that whoever murdered their father will also want to get rid of them. As Malcolm says:
This murderous shaft that’s shot/Hath not yet lighted, and our safest way/Is to avoid the aim/Therefore to horse.
Further, the combination of being in the room beside their father's, which would give them easy and unimpeded access to him, along with their quick flight, makes them look as if they murdered their father. Otherwise, people reason, why would they flee? This deflects suspicion from the real murderer.
In a play with themes that include the folly of murder, as well as what makes a good king, these sons also play a thematic role. Shakespeare makes the point that violence begets violence, illustrating in the play that once someone starts down the path of murdering for personal gain, one must keep murdering and murdering. Arguably, Macbeth should also have killed the sons when he killed the father. But either way, more blood is shed, for Malcolm comes back at the head of an army.
Finally, in a play that weighs the merits of the good versus the bad ruler, Malcolm will emerge as the good ("meek") leader who puts the needs of the people ahead of his own ambitions. He is, not only in blood, but in temperament, the proper heir to the good King Duncan.
According to Lady Macbeth, Donalbain (Duncan's son) was sleeping in the second chamber in Act II, and the second person with him is assumed to be his brother Malcolm. After killing the King, Macbeth told Lady Macbeth,
This is important because this is the point where Macbeth realizes he can no longer say "Amen." He has gone past the point of forgiveness and can no longer pray.
These two characters (sons of Duncan) are important because after they flee, the blame immediately goes on them and Macbeth is next in line for king.