Isaac is representative of a literary type — the "typical Jew" — portrayed as avaricious and obsequious unless he gained power over others; then he could be demanding and imperious. Isaac shares these tendencies but he can be kind, as to Ivanhoe when Ivanhoe is disguised as the Palmer and in need of equipage for the tournament.
Isaac loves two things, his daughter and his money. There always seems to be a struggle when the two are involved in the same transaction. The loss of money is the terrible price he pays for the greater love he bears his daughter.