There are multiple theme statements, or topic sentences, one could create in order to speak to appearance verses reality, the supernatural, and ambition (as seen in William Shakespeare's tragic play Macbeth).
Appearance verses Reality
In William Shakespeare's play Macbeth, the appearance of the dagger and Banquo's ghost appeal to the theme and motif of appearance verses reality.
In William Shakespeare's Macbeth, many motifs speak to the theme of appearance verses reality.
Elements of the supernatural, such as Banquo's ghost, the witches, the apparitions, and the dagger, appear as motifs in Macbeth.
William Shakespeare included elements of the supernatural in his play Macbeth in order to find favor from King James I.
Without the motif of ambition in Macbeth, the play would not exist as the tragedy it is known as.
In William Shakespeare's play Macbeth, the recurring motif of ambition proves to be the one thing which supports Macbeth's desire to obtain and keep the throne.
Choosing a good theme statement for Macbeth depends on what aspect of the play most interests you. You shouldn't feel that you are restricted to "literary" elements, but should take the opportunity to explore ideas that you personally find interesting.
Military Tactics: Much of the play revolves around military tactics, both in large-scale conflicts (Duncan's war against the rebellious Thane of Cawdor and Macduff's army attacking Macbeth) and in smaller surgical strikes (Macbeth's plots to kill Duncan, Macduff's family, and Banquo). In all cases, Shakespeare gives fairly detailed discussions of the precise tactics used and how and why they succeeded. You could discuss how the theme of tactical planning is used to illuminate how characters balance expediency with honor.
Foreknowledge and Free Will: One major debate in theology in Shakespeare's period (and earlier) was how it is possible to balance the notion of foreknowledge with a belief in free will. You could apply this to Macbeth, arguing that the degree to which we believe him guilty depends on our assumption that he has free will, but the prophecies of the witches suggest that his actions were inevitable and foretold.
Legitimacy of Authority: One important question in the period of Macbeth and Shakespeare was the notion of what makes someone a legitimate monarch, whether it was due to brute force, heredity, some form of merit, or popular acclaim. You could investigate this theme by looking at the grounds on which Duncan, Macbeth, and Malcolm respectively claimed legitimacy as rulers.