It is true that Disraeli used that quote in his novel "Tancred", but according to Wikipedia (which is admittedly not inerrant) he also said the same thing in Parliament in support of a bill to allow Jews to sit in the House of Commons. Based on that, I would assume that it was indeed Disraeli's opinion.
What offends me most about the quote is a patronizing attitude by a Christian towards Judaism. It seems to imply that Christians have the whole truth, while Jews have only part of the truth. To me that is both patronizing and belittling.
Perhaps ironically, many members of Parliament felt that what Disraeli said was blasphemous (again according to Wikipedia).