How does Act 2 Scene 4 in Macbeth advance the plot?
Act 2 Scene 4 is a short yet an important scene, not to be left out. The scene between Ross and the Old Man serves three important purposes and one can easily make out how they add to the development of the play.
a) It continues the comparison begun by Lennox in Scene 3 between the human world and the natural world.
"The night has been unruly: where we lay,/ Our chimneys were blown, and, as they say,/ Lamentings heard i'th'air, strange screams of death/And prophesying with accents terrible/Of dire combustion and confus'd events,/ New hatch'd to the woeful time." The old man believes that he has never in seventy years of his life seen "hours dreadful and things strange, but this sore night hath trifled former knowings." Further more the old man also says, 'Tis unnatural, /Even like the deed that's done."
b) The second function of the scene is clear when Macduff enters to bring more news" it indicates the passing of time.
c) The scene highlights Macduff growing in greater prominence, because it allows the audience by the tone of his voice, That Macduff continues to be suspicious of Macbeth's involvement in the crime.
One must also remember that Macduff's role will be very important once Banquo will be murdered.