What is the purpose of Willa Cather's dedication to My Antonia?

The dedication to My Antonia
reads:

TO CARRIE AND IRENE MINER In memory of affections
old and true
Optima dies... prima fugit
VIRGIL

Writers usually choose to dedicate books to people
who have had significant influence on their personal or artistic lives. A dedication can
be a mark of gratitude or admiration.

The quotation from
Virgil, "Optima dies prima fugit" or "the best days are the first to flee" (or "the most
fleeting"; cf. Horace, "Eheu, Postume, fugace, fugace"), suggests that the novel is
about memories of an idyllic past which has disappeared. This fits the theme that the
prarie communities of Cather's choildhood have disappeared, and moreover she herself is
no longer the innocent rural child of her past. The narrator's journey to the past
echoes this theme, in that Antonia is grown and married, and he cannot retrieve the
relationship or circumstances of his past.