what was macbeth's ambition?

Answer 1

The acquisition of power, as I remember.

Answer 2

That is not so simple. Why? First, he probably would not have done anything if he hadn't been pushed hard by his very ambitious wife because people at that time believed that ghosts usually were tempters from hell and that witches were very evil so, just like Hamlet, he had doubts about the prophecies that said he would be king.

Then again maybe he was a power-hungry young man who had some doubts but really planned to get to be king.

Actors could play it either way. Maybe he just wanted Lady Macbeth to shut up and leave him alone.