The “if only” usually refers to the marriages of Fanny & Henry, Mary & Edmund. What happiness for them all! What fun for the readers to enjoy Henry’s and Mary’s felicity, and to see Fanny and Edmund learn to laugh at themselves, as Mr. Darcy did in Pride and Prejudice.
But this is impossible. As Austen wrote the story, tragedy was inevitable. Although she convinces us that Fanny and Henry could be truly happy together, she states that Fanny would only have married Henry after “a reasonable period from Edmund’s marrying Mary.”1 And, sadly, it seems that Edmund and Mary would not have been happy together.
In contrast to Henry, who, within a short time of falling in love with Fanny, began to change his actions2, Mary did not change for love of Edmund, although her affection continued for many months. In conversation, Henry moderated his tone and topics to Fanny, but Mary sharpened her tongue against Edmund. She ridiculed his principles rather than trying to understand them.
Also, Mary despised Edmund’s profession and would have been discontent with his income. Whereas marriage to Fanny would have been Henry’s moral salvation, marriage to Mary would have been Edmund’s moral condemnation. And Henry’s moral salvation—through Fanny, at least—could only happen by that sacrifice of Edmund.
And we all know what happens when neither of these couples marry. A tragedy.3
1Chapter 48, Mansfield Park.
2I chose “actions” as distinct from “principles”. Henry did think about serious subjects more seriously while courting Fanny, but ultimately did not change his principles.
3Although Edmund did suffer deeply, this was a tragedy primarily for the Henry and Mary, as, ultimately, Fanny and Edmund lived happily ever after.