In Voltaire's novel, Candide, the three themes that stand out in the old woman's tale for me are:
- one cannot depend that things will always stay the same: being rich and famous one day does not necessarily guarantee that this will not change
- even though we may believe our troubles are awful, there is always someone with difficulties worse than our own
- even when we hate our lives and think it would be better to be dead, we still hold on to life; while there is life, there is still hope
Voltaire wrote Candide in the form of a parody (a form of satire) directed toward Gottfried Wilhelm von Leibnitz and his philosophy on optimism—we see this in Pangloss' teachings and attitude which continually return to his belief that in every situation, "this best of all possible worlds." In other words, everything is as it should be.
My sense is that more than having an unshakable belief that things are always for the best no matter the circumstances, I imagine that Voltaire believed a realistic approach to life was more valuable. This is not to say that people should not have an appreciation for positive things in their life, but one need not appreciate difficulties and hardships, seeing them as positive parts of our human existence.
Because Voltaire is making fun of optimism under every circumstance, I believe the old woman's story, and the themes found there, encourage the reader to feel positive when appropriate, and sad when a situation dictates it. Bad things happen, but this is not something we must accept without resistance or feeling.
The ideas that things can change at any time, there are always other people with problems worse than our own, and regardless of our heartaches, life is still valuable are realistic concepts that follow the advice that the old woman shares: she is not silly enough to believe that watching her mother murdered was "the best of all possible worlds." And this is exactly what Voltaire was trying to share with his audience. The author uses the character of the old woman to allow us to feel honestly about the things that fill our life: thankful when things are good, and hopeful when things go awry.