How do you compare macbeth here (talking to the murders) to macbeth before the murder of duncan

Macbeth is a lot more certain and has more confidence within himself as apposed to before his murder of the late King Duncan. He is fearless, as the Witches (or Weird Sisters) has proclaimed he could not be harmed by any son of a woman. This is the significance as Macduff is born by Cesarean section, not by "natural" birth from his mother.