His parents believed that the priesthood was his 'destiny'. [=that he would or should become a priest because fate or God intended it]
They were living in a time when expansion to the Pacific was regarded by many people as the 'Manifest Destiny' of the United States.
She felt that 'destiny' [='fate'] had decided that she would one day be President.
(..) evil men die and we cheer her for it. And she grows more powerful and more sure that she is good and right. She believes her destiny is to build a better world for everyone. If you believed that... if you truly believed it, wouldn't you kill (..)2019 TvShow: Game of Thrones Title: The Iron Throne Season: 8 Episode 6