Candide by Voltaire is a story about Candide, a young man indoctrinated into blind optimism by his mentor Professor Pangloss. He receives his teachings while being hosted by the Baron; however, his stay is cut short after he falls in love with Cunegonde, the daughter of the Baron (who is opposed to the relationship). While in the real world, he experiences much hardship and encounters a lot of strife. He experiences first hand the effects of war as a Bulgarian soldier. He begins to question the optimism taught to him by his mentor during his younger years. He doubts his mentor’s mantra (“best of all possible worlds," meaning all is for the best) because he is unable to comprehend how all the bad experiences in life are positive. Candide eventually dismisses blind optimism, but does not lean towards pessimism either, and instead remains indifferent to the two extremes.
a commentary on the human condition. You might translate that to an assertion: "This is what it means to be human." If that's the case, then what it means to be human is to suffer, to take part in ignoble action, and to believe things that don't really work in the world.
If I had to boil down some of the other messages, I'd say he's saying, "Organized religion is often stupid," "War isn't noble, it is brutal," and "Much philosophy is arrogant stupidity." The best example of this last point is Pangloss.