Symbolism, Imagery, Allegory
Ugly Stereotype... Of Ugly Stereotypes
We don't usually defend stereotypes. About 99.99% of the time, they're gross relics of a less enlightened time, and we feel icky reading them. But in the case of Don Isaachar, Voltaire isn't just giving us another Jewish stereotype—because of the context of Candide, we can see that Voltaire is giving us a stereotype of... religious stereotyping.
We'll break it down.
Cunégonde's Jewish owner, Don Isaachar, functions as a symbol for all the prejudice we see in Candide. Isaachar, in particular, is a target for anti-Semitism: he's portrayed as wealthy, greedy, and morally depraved—par for the course in the horrible-Jewish-stereotype game. Like other religious figures, such as the Inquisitor and the Abbé, Voltaire depicts Isaachar as self-serving and unkind.
While Voltaire singles out and criticizes a number of religions in Candide—notably Judaism, Christianity, and Islam—his standpoint is more generally a rejection of religious factionalism and violence than of any one religion in particular. In portraying negative stereotypes of Jews, Christians, and Muslims, Voltaire actually satirizes prejudice (and prejudiced people's ways of constructing stereotypes) itself.