Little Women is in dialogue with John Bunyan's allegory of Christian faith The Pilgrim's Progress, and so it's not surprising that direct characterization is one of Alcott's favorite techniques. After all, in allegories, we're usually told pretty directly what each character represents. In this novel, the narrator tells us right away that Meg has a tendency to be materialistic, that Jo is the tomboyish one, that Beth is shy, and that Amy is vain. There's not much guesswork going on here.
As each of the March sisters becomes an adult, she re-creates the family structure that Marmee established. Of course, each sister gives it a twist of her own; Jo's boarding school for boys isn't much like Meg's snug cottage or Amy's mansion. We learn about each sister by watching how she adapts Marmee's domestic wisdom to her own situation and inclinations.
The March girls are who they are because of the values they've been taught in their family. They'll tell anyone who asks that they're patriots, that they value hard work and discipline, that life is like a pilgrimage, and that money can't buy happiness. Part of the reason Laurie is so convinced that he needs to marry one of the March sisters is that he becomes convinced of their value system; his thoughts and opinions are in sync with theirs.