I have listed what I believe are the most significant quotes from Acts 1 and 2, with brief explanations as to why they are important:
Act 1:
Fair is foul, and foul is fair:
This is uttered by the three witches in scene 1, using alliteration for emphasis. They plan to meet Macbeth on the heath later after the fighting has stopped, and begin their malicious manipulation. The words introduce the theme of paradox and equivocation, which is the technique used by the witches to deceive Macbeth throughout the play.
...For brave Macbeth--well he deserves that name--
Disdaining fortune, with his brandish'd steel,
Which smoked with bloody execution,
Like valour's minion carved out his passage
Till he faced the slave;
Which ne'er shook hands, nor bade farewell to him,
Till he unseam'd him from the nave to the chaps,
And fix'd his head upon our battlements.
This quote is from scene two and is a sergeant's testimony of Macbeth's courage, loyalty, and his relentless pursuit of his king and country's enemies. The metaphors and similes create the impression of an honorable man who deserves respect.
...And with his former title greet Macbeth.
Duncan makes this declaration at the end of scene two. He awards the title of the captured traitor, the thane of Cawdor, as a reward to Macbeth for his valour on the battlefield. This is significant because the witches later greet Macbeth with this title, also claiming that he would be 'king hereafter.'
All hail, Macbeth, hail to thee, thane of Cawdor!
All hail, Macbeth, thou shalt be king hereafter!
These greetings are extended by the second and third witches in scene 3. These are the predictions which spur Macbeth's ambitions. When he later discovers that the first prediction has come true, he believes that it is also his destiny to be king.
Thou shalt get kings, though thou be none:
This declaration, by the witches, is addressed to Banquo. It is important since it is this prophecy which mostly informs Macbeth's decision to have Banquo and his son, Fleance, murdered later. They are both seen as a threat not only to Macbeth but also to his lineage.
If chance will have me king, why, chance may crown me,
Without my stir.
Macbeth utters these words in an aside after Ross had informed him about his being awarded the title, thane of Cawdor. He muses that if it should be his destiny to be king, that he might achieve the position without any action on his part. The quote indicates Macbeth's emphatic belief in the witches' predictions.
Glamis thou art, and Cawdor; and shalt be
What thou art promised: yet do I fear thy nature;
It is too full o' the milk of human kindness
To catch the nearest way
Lady Macbeth expresses her fear that her husband will not be ruthless enough to murder Duncan. She cannot wait for him to arrive so that she may encourage him.
...look like the innocent flower,
But be the serpent under't. He that's coming
Must be provided for:...
These are lady Macbeth's instructions in scene 5, after her husband's arrival. She tells him, by using an apt simile, to act in a convivial manner whilst plotting the king's assassination. He should not act in a suspicious manner, for Duncan must be taken care of, innuendo for the fact that he must be murdered. These lines indicate Lady Macbeth's perfidy. Ambition has made her ruthlessly determined to usurp the crown.
We will proceed no further in this business:
Told to lady Macbeth in scene 7. Macbeth has reconsidered his decision to murder his king but is soon persuaded by his wife to proceed. The line indicates that he still has integrity and also fears that they might fail in their pernicious venture. It also shows that, at this juncture, Lady Macbeth is much more heartless than her husband.
Act 2:
Is this a dagger which I see before me,
The handle toward my hand?
This quote in scene 1, indicates Macbeth's state of mind. He is completely overwhelmed by the evil which he is about to commit and hallucinates seeing a dagger leading him to Duncan's chamber. The entire monologue in this instance indicates Macbeth's terrible travesty. He is tortured by the thought of killing his king and believes that the images of death and destruction he sees are all false, created by the anxiety he is experiencing, which he calls 'a heat-oppressed brain.'
I'll go no more:
I am afraid to think what I have done;
Look on't again I dare not.
This quote indicates that Macbeth has not reconciled with the fact that he has committed such a terrible deed. He has brought the daggers with which he killed Duncan with him and Lady Macbeth has instructed him to return them. He cannot go back and witness the carnage again. he is filled with trepidation. Lady Macbeth then returns the instruments of murder herself and places them on Duncan's guards, implicating them.
A little water clears us of this deed:
This quote from Lady Macbeth is a euphemism and indicates the obvious difference between her and her husband's attitudes to the murder. She is almost flippant about it, whilst Macbeth is tortured and believes that he will never wash Duncan's blood off his hands, and it will, instead, taint all the oceans. He is overwhelmed by guilt.
Had I but died an hour before this chance,
I had lived a blessed time; for, from this instant,
There 's nothing serious in mortality:
Macbeth's facetious and dishonest remark in the form of a juxtaposition here, indicates his depravity. His purpose is clearly to deceive others to believe that he feels great sorrow at this most heinous crime. The dramatic irony is obvious.
O, yet I do repent me of my fury,
That I did kill them.
Macbeth confesses that he has killed Duncan's two guards in a moment of passionate fury at their malice. He states that he had lost all reason in that instance. The true purpose, however, was to avoid all suspicion. The guards could have implicated him or his wife.
Malcolm and Donalbain, the king's two sons,
Are stol'n away and fled; which puts upon them
Suspicion of the deed.
Macduff expresses, in scene 4, the fact that Duncan's two sons have escaped, which creates the suspicion that they are responsible for their father's murder. In fact, they were in fear of their own lives and decided to leave, lest they also become victims of the evildoers' plot.
Well, may you see things well done there: adieu!
Lest our old robes sit easier than our new!
Macduff tells Ross, also in scene 4, quite sarcastically, that he is not going to Scone to witness Macbeth's coronation, but wishes him well in going there. His later remark reveals his suspicion of Macbeth for he expresses the sentiment that they may find that their erstwhile positions under king Duncan were better than they would now be under Macbeth's rule. He clearly also feels vulnerable and threatened.
Your essay:
Begin with a strong thesis statement in your opening paragraph in which you present the idea of how the occurrences in these two acts determined and affected the development of all the events in the play.
You can use the quotes to construct paragraphs which would relate the most pertinent occurrences in the two acts. The quotes also provide insight into the characters' mindsets during such events. Each paragraph can be constructed around one or two quotes. The quotes also provide a linear sequence of events which would accurately describe how Macbeth and his wife's plot developed.
Your conclusion can provide a brief summary regarding the fact that the Macbeths had achieved their pernicious purpose and some suggestion as to how things may develop further. Look especially for the irony in their actions.