Certainly a complex character whose attributes and failings have long been debated, Macbeth appears first as a great warrior, a general in the army of King Duncan of Scotland. In Act I, a bleeding sergeant reports on Macbeth,
For brave Macbeth—well he deserves that name—
Disdaining fortune, with his brandish'd steel,
Which smoked with bloody execution,
Like valor'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 [Macdonaldwald's] head upon our battlements.(1.2.18-25)
Clearly a warrior of uncommon valor, Macbeth fights with a surety that is in marked contrast to his superstitions in the next scene. There, on a heath near Forres, where "So foul and fair a day I have not seen," as Macbeth observes, this brave warrior witnesses three witches and questions them about their prophetic greeting, but they vanish. Banquo, who is with him, notices that the consummate warrior Macbeth shakes,
Good sir, why do you start, and seem to fear
Things that do sound so fair? (1.3.55-56)
In addition, his mind is also visibly shaken and he has lost his surety as Macbeth worries about the witches' predictions in an aside,
Two truths are told,
As happy prologues to the swelling act
Of the imperial theme!—I thank you, gentlemen.
[Aside.] This supernatural soliciting
Cannot be ill, cannot be good. If ill,
Why hath it given me earnest of success,
Commencing in a truth? I am Thane of Cawdor.
If good, why do I yield to that suggestion
Whose horrid image doth unfix my hair
And make my seated heart knock at my ribs,
Against the use of nature? Present fears
Are less than horrible imaginings:
My thought, whose murder yet is but fantastical,
Shakes so my single state of man that function
Is smother'd in surmise, and nothing is
But what is not. (1.3.138-153)
Initially brave, fierce, and a man of action, Macbeth encounters the supernatural world and becomes uncertain, visibly shaken, and superstitious. Further, having given credence to the predictions of the three sisters, Macbeth decides to accelerate his fate and slay Duncan, but his wife tells him he is "too full o'th'milk of human kindness" as his conscience causes him anxiety about killing the king. Waivering thus, he deliberates in a long soliloquy in Scene 7.
Personally I think that Macbeth is an enthralling character in so far as he is divided or rather torn between desire and reason. Unfortunately for him his mind is infected that is why he cannot tame his volitions and his urges. In other words his tragic flaw (hamartia) knows an upsurge and he is unable to resist it.
He is compelled to yield. Of course we know that Macbeth will be punished at the end of the play (owing to the principle of nemesis or divine wrath). However at the beginning of the play, Macbeth is presented as a good character (but we might notice that he is absent). In this context his absence is a pivotal element to the overall understanding of the play because when encountering the three witches his true face is unveiled. Thus I think that we have to underline the fact that his apparition changes the vision that the spectator could have of him. Before his apparition the spectator could have thought that he was a good and brave general. On the one hand he is presented as a good general, on the other he is described as perverted by the foreboding of the three witches. In short Macbeth was predisposed to be a murderer. Evil is an inherent part of his nature.
I hope it will be useful.