Question

Macbeth’s second visit to the witches and the predictions he hears make him

Answer 1

The predictions make him more bold and cruel, as Hecate is trying to make him overconfident. He becomes especially bold when the final apparition says that 
'Macbeth shall never vanquish'd be until
Great Birnam wood to high Dunsinane hill
Shall come against him.'

Lady Macduff becomes aware that doing harm is often laudable, and doing good can lead to 'dangerous folly,' meaning that sometimes bad deeds are done by bad people and go unpunished, regardless of our intentions.