When Macbeth starts, there is a terrible storm and the audience wonders what may be in store. The witches present the first scene and it is apparent that the storm foreshadows far worse to come; in fact, the witches chant "fair is foul and foul is fair" in Act I, scene i (line 10). After the witches disappear, and before meeting Macbeth, the audience learns from Duncan and his men that Macbeth is "brave" and "worthy."
When Macbeth enters, his first comment is that he has not seen "so foul and fair a day" (I.iii.38) meaning that the weather is appalling but at least he and Banquo have had success on the battlefield. The two men are bemused by the witches who reappear, especially when they talk of the likelihood that Macbeth will be awarded the title of Thane of Cawdor and even go as far as to say that he will be king.
It is apparent that Macbeth is unsettled by the witches' talk and it is not long before the very title that the witches spoke of (Thane of Cawdor) is presented to a shocked Macbeth who immediately believes that there may be truth in the witches' words and he may be king after all, although Banquo does warn him not to put too much store in the promises and claims of the "instruments of darkness (124). So, Macbeth's transformation from decorated and valiant soldier has already started and his "earnest of success" (132) creates an internal conflict which starts to eat away at his very soul.
Macbeth was a powerful warrior and a loyal subject of the king. However, since he changes so much and so quickly in response to the prophecy, we can also suspect his character is malleable.
At the beginning of the play Macbeth has won recognition for his bravery in battle and his defeat of the King of Norway and the rebellious Macdonwald. He is described as brave and fearless, and he is yet to become ambition. In fact, when the witches first give him his prophesy he is confused rather than extatic. THis of course quickly change as Macbeth and Lady Macbeth become more and more ambitious, power being their ultimate goal.