One of the key themes of Little Women is the importance of family. The March sisters are extremely close to one another and to their parents. Receiving a letter from their father, who is away from home in the army as a chaplain, is a treat that raises the girls's spirits.
Another theme is the need to take on responsibility during difficult times and to maintain a strong outlook in the face of adversity. It is important to remember two things about the story. First, the March girls are living during a war. Many, if not most, of the men are away. Second, the March family is old and established. They once had money, but are now poor in comparison to their extended family. Yet, they are encouraged to deal with life's difficulties and not complain. As the title of the novel suggests, they are to act as "little women" with maturity beyond their actual years.
It does not mean that the girls do not want to have nice things or strive for more exciting times. However, it is important for them to remember to be thankful for what they have. There are religious overtones to this message that can be seen in the game the girls play as youngsters, Pilgrim's Progress. Marmee tells them that,
Nothing delighted you more than to. . .let you travel. . .from the cellar, which was the City of Destruction, up, up, to the housetop, where you had all the lovely things you could collect to make a Celestial City."
In the game, the March girls aspire to travel from the City of Destruction to the Celestial—or heavenly—City. Moreover, when the story opens, they are living during a time of war and destruction. Young men and even many older men, like their father, are away in the army, so the women that they have left behind must fend for themselves. It is not a time to complain, but to deal with life as it comes. As Meg tells her sisters in the very first chapter, this is the reason that Marmee asked them to forego presents at Christmas; it will be a hard winter for everyone, and there is no time for frivolity.
Meg says, "our men are suffering so in the army." They can do their Christian and patriotic duty by acting bravely and recognizing how difficult things are for everyone, and making the according sacrifices.