It is true that Mansfield Park is very much
a novel of morality, however I could never sympathise with the view that it is somehow morally
archaic and incomprehensible. If the moral
dilemmas in it are transplanted into comparable modern settings, they still stand as valid and the resulting actions of the various characters emerge in the same light as they are presented in in the novel.
Let's take the two moral conflicts pivotal to the latter part of the book. The first, between Henry Crawford and Fanny Price, and the second between Mary Crawford and Edmund Bertram:
Let's assume that Henry and Fanny are alive today, and that they're involved in an am-dram production of a slightly racy play, with the possibility of intimate scenes between the lead characters. Would you, after having watched him scheme to be included in all the more interesting exchanges, and flirting to the point of hurting their feeling with practically all your friends in the world, go out with him? You'd have to be a dimwit. And Fanny, straightlaced and mousy though she might be, is no fool. Her aim in life is not only to marry, but to have a good marriage, which she doesn't think she can have with a flirt and womaniser (can't blame her, myself).
Now let's take a look at the prospects of Edmund and Mary. He's training very seriously for a profession he's quite passionate about, a profession she holds in contempt and considers good material for jokes. Regardless of the profession itself, and the moral implications of her contempt for it, would anyone consider this a good foundation for a marriage?
Running through most of Austen's work is the belief that doing right is the key to happiness in life, as opposed to "doing well". In Pride and Prejudice Austen went so far as to rewrite the last few chapters of the book so that the renewed understanding between Elizabeth and Darcy does not stem from a breach of confidence by Mrs. Gardiner - she would have considered it a terrible omen for the beginning of their life together. In Northanger Abbey the comic "heroine" Catherine makes a good match through no other virtue than being a decent and honest young woman.
Nowhere is this ideal illustrated more forcefully than in Sense and Sensibility, however. Elinor, who submits to the everyday drudgery of social niceties and nosy connections, through her self sacrifice, self possession and constant care for the feelings of others and for propriety, gains enough merit to get her man. Marianne, contemptuous and selfish, doesn't, and is only redeemed enough to be given any measure of happiness in life through her brush with death and the subsequent repentance.
So, it is not only moral superiority, but an honest belief in the inseparable link between moral fortitude and happiness which guides Austen in her characterisation of Fanny. She doesn't get Edmund by default, or as a prise for her stolidity - she gets him in the natural course of life bringing two people with large amounts of common sense together. No matter her charms, Edmund would not have been happy with the prattling Mary Crawford.
Neither is the analogy between Fanny Price and Mary Bennett in any way solid. Mary is a caricature, designed to highlight the evils of vanity - she is clearly putting her meagre skills to academic ends because she cannot stand out amongst her sisters in beauty. Her interest in intellectual pursuits is revealed as incincere in the final note made about her in the novel. Fanny on the other hand takes a great deal of genuine pleasure in having herself and everything else around her just so - a fact revealed by her gentle reorganisation of the daily routine at her parents' house during her visit there.
Another thing that sets Fanny apart from the rest of the characters in the novel, and marks her out as their superior, is her strong and enduring affections. Her attachment to her brother is a commendation of the power of her heart, an attachment which none of the Bertram siblings share. She also has more of affection and respect towards her uncle than either of his own daughters, a fact that he realises only too late (which is his own hubris in this tragedy, but that's another writeup).
This ability to give her heart fully and warmly, while at the same time not to stray from the (common sense as well as moral) straight and narrow, is what makes Fanny Price a superior character - together with her beauty, her intellect and her other talents. I can't say that for me, as a 20th century reader, she is the most attractive of Austen's heroines - she has none of Emma's sparkle or of Elizabeth's humour and intelligence. But I dare say she'd make a good friend, if I ever met her, and I never put the novel down without feeling that I have been given a useful and gentle lesson in how to tackle the everyday difficulties of my own life.