One of the major divides in Mansfield Park is between action and passivity. Characters are largely defined by their active or their passive natures, and this division extends over into other contrasting traits: talkative characters versus silent ones, moving ones versus still ones, etc. Fanny, in particular, is a poster child for passivity. She watches from the sidelines while others lead messy, active, and exciting lives. Though it may seem safer to remain passive, passivity carries its own risks. Silent, passive characters are frequently misunderstood by others, who are forced to make faulty assumptions about them.
Edmund can actually be described as a passive character since he acts very slowly and often fails to act at all.
Despite their flaws and their misguided (even bad) actions, the active Crawfords are more admirable than the book's more passive characters, like Fanny.