It might be argued that marriage is the core of Jane Austen's favorite themes. There are many kinds of marriages depicted in Mansfield Park. One is the spiritually and monetarily frugal and childless marriage of Reverend and Mrs. Norris. Another is the wealthy privileged and indolent marriage of the Bertrams. Yet another is the hopeless and ill-conceived poverty-stricken marriage of the Prices. Another is the proposed marriage of folly and corruption between Henry Crawford and Fanny. Still another is the marriage of manipulation, convenience and abandonment between Maria Bertram and naive, betrayed Mr. Rushworth:
[Maria] loved [Henry]; there was no withdrawing attentions avowedly dear to her.
One final marriage to consider is the proposed one of love and genuine accord between Fanny and Edmund. They bring out the best and noblest in each other. They conduct their lives, actions and ideas based on sound moral ethics and principles. They each think of and give to others. They both shun immoral behavior such as that of Henry Crawford (although Edmund was beguiled by the beauty and lively spirits of Mary Crawford). They both have the respect and love of Sir and Lady Bertram.
[Sir Thomas] prizing more and more the sterling good of principle and temper, ... [and] the high sense of having realised a great acquisition in the promise of Fanny for a daughter,
They both make things a little better for having been in a place or cared about a person.
could [Henry] have found sufficient exultation in ... working himself into the esteem and tenderness of Fanny Price, there would have been every probability of success and felicity for him.
These are the characteristics that unite to make a good marriage in Jane Austen's world (and, I dare say, in our world).