There is no real ending. It's just the place where you stop the story.
- - - Frank Herbert
The closing line of your book might represent a heartfelt good-bye, a sense that life goes on or an acknowledgment of all that came before, like a thank-you note. Or a fuck you note. It might be a way to say au revoir rather than good-bye. It may suggest a triumph that ends the book on a positive note or it may leave readers with a situation that will never be resolved, like unrequited love. There may be a sequel in the works or this may be the end of the story. Whichever it is, your book is finished but the closing line suggests that the story and the lessons will continue to impact the reader.