Read the quotation from "To the King's Most Excellent Majesty." "May George, beloved by all the nations round, Live with heav'ns choicest constant blessings crown'd!" Wheatley uses the word crown’d to express the idea that the king
Wheatley uses the word to express the idea that the king deserves to always be blessed with good things and with goodness. It's like a pun because the crown is also the king metaphorically and the crown is also a real thing wore by the king and it is also a metaphor for something that is bestowed upon you, in this case good things.
