In the beginning, Macbeth is a virtuous man, or at least interpreted as one by those who know him. He has been thinking of power, but has not yet made any decision upon it, and it is really just a thought, a dream even, in the back of his head, which he seems to have no real intention of pursuing. One may see how Macbeth is virtuous when an injured Captain is coming back from the front, and tells Duncan and Malcolm about the battle:
"And Fortune, on his damnèd quarrel smiling, / Showed like a rebel 's whore: but all 's to weak; / For brave Macbeth (well he deserves that name), / Disdaining Fortune, with his brandished steel, / Which smoke with bloody execution, / Like Valour 's minion, carved out his passage, / Till he face the slave; Which ne 'er shook hands, nor bade farewell to him, / Till he unseamed him from the nave to the chaps, / And fixed his head upon our battlements." (Act One, Scene II, l.14-24 Shakespeare)
In this story told by the captain, Macbeth is a virtuous man. The Captain qualifies Macbeth as brave and even comments on how Macbeth "deserves that name". This may be considered Macbeth initial and noble stage, before power corrupted him, to the point of committing numerous atrocities for the sake of power. Macbeth