In Book 1, Chapter 4, Lady Booby and Joseph Andrews begin to spend more time together—and the gossipers of the London elite begin to take notice. Fielding takes this opportunity to emphasize Andrews's obliviousness and to foreshadow Booby's infatuation:
But whatever Opinion or Suspicion the scandalous Inclination of Defamers might entertain of Lady Booby’s innocent Freedoms, it is certain they made no Impression on young Andrews, who never offered to encroach beyond the Liberties which his Lady allowed him. A Behaviour which she imputed to the violent Respect he preserved for her, and which served only to heighten a something she began to conceive, and which the next Chapter will open a little farther.
By this point, the reader would be right to suspect that something is afoot, in at least one direction, between Booby and Andrews. Fielding's emphasis on Andrews's respectability and his nods to Booby's little "something" that she begins to feel both serve to foreshadow the one-sided romance that will unfold over the rest of the novel, though the language is shrouded in euphemism—the reader can only guess what little "Liberties" Booby allows Andrews.
Joseph Andrews is, at its heart, a love story, and Fielding navigates between portrayals of genuine, virtuous love (like that of Andrews and Fanny) and sinful, indulgent passion. In this passage, the reader is privy to the evolution of the latter form of "love," in all its scandalous glory.
In Book 3, Chapter 4, Wilson and Abraham Adams discuss Wilson's son, who was stolen from Wilson as a child. In a critical moment of foreshadowing, Wilson shares the key feature by which he could immediately identify his son:
The gentleman answered, he should know him amongst ten thousand, for he had a mark on his left breast of a strawberry, which his mother hand given him by longing for that fruit.
Wilson's assurance that he could identify his son even in adulthood foreshadows his son's return later in the novel: Joseph Andrews himself bears a birthmark in the shape of a strawberry, and in Book 4, Chapter 15, after Lady Booby reveals the mark, Wilson realizes that Andrews is his son.
Questions of family and parentage abound in Joseph Andrews, and Fielding spends much of the novel emphasizing just how arbitrary class status can be in England—your lot in life should be determined by who you are raised to be, Fielding implies, regardless of who your biological parents are.
This setup and reveal of the strawberry resolves the question of Andrews's lineage and enables Fielding to keep the plot moving along quickly once the truth has been revealed—Fanny cannot be Andrews's sister, and they can therefore get married with no objection: the story of Joseph Andrews can finally conclude with a happy ending.