[Isaac's] doubts might have been indeed pardoned; for, except perhaps the flying fish, there was no race existing on the earth, in the air, or the waters, who were the object of such an unintermitting, general, and relentless persecution as the Jews of this period. Upon the slightest and most unreasonable pretenses, as well as upon accusations the most absurd and groundless, their persons and property were exposed to every turn of popular fury; for Norman, Saxon, Dane, and Briton, however adverse these races were to teach other, contended which should look with greatest detestation upon a people whom it was accounted a point of religion to hate, to revile, to despise, to plunder, and to persecute. [...]
The obstinacy and avarice of the Jews being thus in a measure placed in opposition to the fanaticism and tyranny of those under whom they lived, seemed to increase in proportion to the persecution with which they were visited; and the immense wealth they usually acquired in commerce, while it frequently placed them in danger, was at other times used to extend their influence, and to secure to them a certain degree of protection. On these terms they lived; and their character, yet obstinate, uncomplying, and skilful in evading the dangers to which they were exposed. (6.63-64)
Ivanhoe's depiction of its Jewish characters is highly problematic. On the one hand, Scott seems sympathetic to the constant, horrible prejudice that Jewish people suffered in medieval Europe. He also explicitly states that both Normans and Saxons took advantage of religious hatred to rob the Jews shamelessly. Scott clearly doesn’t support the anti-Semitism that many of his characters in this novel express.
At the same time… what's going on with that second paragraph? Scott says this constant prejudice and abuse made the Jews as a people greedy, paranoid, and stubborn. That's a pretty big generalization, don’t you think? All Jews are this way? So Scott condemns prejudice against the Jews, but he also repeats some terrible Jewish stereotypes in his characterization of Isaac and of Jewish people in general. For more on this contradiction, check out "Characters: Isaac of York."