Final answer:
King Duncan bestows the title of Prince of Cumberland upon his son, Malcolm, making him the heir to the Scottish throne in Shakespeare's play Macbeth.
Step-by-step explanation:
The new title that King Duncan bestows upon his son, Malcolm, is the Prince of Cumberland.
This title is significant because it designates Malcolm as the heir to the throne of Scotland, an honor that sets in motion a chain of events leading to the central conflict within Shakespeare's play Macbeth.
King Duncan declares this title as a marker of honor and nobility, suggesting that not only Malcolm but all those worthy will shine like stars with the signs of nobleness.