This famous speech occurs in Act V, Scene 5, when Macbeth is awaiting the battle that will prove his undoing. He has just learned that his wife has committed suicide, consumed by guilt, and his response is a remarkably bleak reflection on life. "Tomorrow, and tomorrow, and tomorrow" evokes the relentless, numbing "petty" pace at which the days go by. Macbeth says that life is simply a march to our deaths, with no more meaning. He compares life first to a play, in which we are just actors that pass briefly upon the stage, and then to a "tale/Told by an idiot" which, for all its "sound and fury" has no deeper or lasting meaning. This is a profoundly bleak view of life, one which is held by a man who has, turned his back on his own humanity to fulfill his ambitions, and is about to be destroyed himself.

A juxtaposition is a literary technique in which two or more ideas are placed side by side in order to compare, contrast, and emphasize a given subject. Throughout Macbeth's famous soliloquy, Shakespeare not only juxtaposes light with dark and sound with silence, but he also explores the concept of time through juxtaposition. Macbeth is essentially saying that our meaningless lives are short-lived and transient. As each day goes by, individuals come closer to their untimely deaths, until they are heard from no more. Macbeth begins by repeating the word "tomorrow," then mentions that each day progresses until the "last syllable of time." Macbeth then comments on "our yesterdays" that eventually result in our dusty deaths. He then proceeds to compare one's life to a brief hour onstage before they are heard from no more. Shakespeare compares the past, present, and future throughout Macbeth's soliloquy to emphasize our fleeting existence. By comparing one's life to a brief hour on stage, Shakespeare highlights our transient presence on earth. 

In this soliloquy, Macbeth expresses the despair he feels upon Lady Macbeth's death.  This despair is darkened further by the sense of meaninglessness and doom as Macbeth contemplates his empty future which was once so full of promise and ambition.  The juxtapositions in the passage serve to intensify this portrayal of despair.  

For example, there is the juxtaposition of light versus dark.  The past is marked by "lighted fools" while the future ends in the darkness of death.  "Out, out, brief candle!" describes the individual's death.  The interim, life, is "but a walking shadow."  Darkness can signify the corruption of Macbeth's soul in the course of the play's events as well as the growing influence of the "weird sisters" (demonic forces).  

Another juxtaposition is sound and silence.  There are parallels in the descriptions of life as a poor player strutting upon the stage only to be "heard no more" and life as a tale told by an idiot, "full of sound and fury,/Signifying nothing."  In both descriptions, Shakespeare juxtaposes the sounds of a life with the silence of death.  Ultimately, the noises of life mean "nothing"--just as the ambitions of Macbeth came to nothing and end in his death.