In this final soliloquy we uncover the ultimate tragedy of Macbeth. "It is the tragedy of the twilight and the setting-in of thick darkness upon a human soul" (Dowden 66). Macbeth's heinous acts throughout the play have resulted in his last, horrible conclusion about life: it is utterly meaningless. Our days on this earth serve no purpose other than to thrust us toward "dusty death." Life is a seemingly endless and depressing succession of bleak days creeping along at a "petty pace." Our time on this earth is so unsubstantial that it can only be compared to a shadow; so unreal that it can only be compared to a stage on which frets a pitiful actor. When the play is over his character disappears into nothingness, and has left nothing significant behind.
Macbeth's feelings toward Lady Macbeth in this soliloquy are not as clear as the overlying theme. As seen above in the notes, there are four, and possibly several more, opinions regarding Macbeth's initial reaction when he hears that his wife is dead. Those who take the first line to mean "she would have died at sometime, either now or later" usually argue that it illustrates Macbeth's callous lack of concern for Lady Macbeth. However, it seems more likely that the line is a combination of meanings (1) and (4) cited in the notes above:
[Macbeth] has said (in Scene III of this act) that the battle will cheer him ever after or disseat him now. Up to this time he had expected to win the battle; he was ready to laugh the siege to scorn when interrupted by the cry of women. And may not his visionary thought have pictured the victory as restoring him to the man he once was? He pauses on the word "hereafter" (there are two missing feet in the meter), and realizes that the time will never come now. Sadly he reflects that if it could have been, if he could have gone back, then there would have been time to consider that word, death, and to mourn properly. But now, now that there is to be no victory, and no going back, now that she is gone the tomorrows creep on with their insignificant slow pace to the last syllable of recorded time. (Coles, Shakespeare Studies: Macbeth, p.269-79)
REFERENCES
Coles, Blanche. Shakespeare Studies: Macbeth. New York: AMS Press, 1969.
Shakespeare, William. The Tragedy of Macbeth. Nicholas Brooke, ed. Oxford: Clarendon Press, 1990.
Shakespeare, William. The Tragedy of Macbeth. George Lyman Kittredge, ed. Toronto: Blaisdell Publishing, 1966.
Shakespeare, William. The Tragedy of Macbeth. W.F. Langford, ed. Toronto: Harcourt Brace Jovanovich, 1967.
Shakespeare, William. The Tragedy of Macbeth. Kenneth Muir, ed. London: Methuen and Co., 1951.
Shakespeare, William. The Tragedy of Macbeth. John Dover Wilson, ed. Cambridge: UP, 1968.

