His first lines on stage are "
So fair and foul a day I have not seen," which mirrors the lines the witches repeated in Act 1 Scene 1. Here, it seems to me, Shakespeare is establishing that Macbeth is already
under the control of at least
influenced by the witches - bear in mind Macbeth enters just after the witches have completed their magic spell. So, at this point in the play, Macbeth is a good man who seems to be under the control of dark forces.