Robert S. Wistrich, who devoted his four-decade scholarly career to dissecting anti-Semitism, from the biblical Haman, who warned King Ahasuerus of Persia against strangers whose “laws are diverse from all people,” to modern Islamist extremists who deny Israel’s right to exist, died on May 19 in Rome. He was 70.

The Hebrew University in Jerusalem, where he taught since 1982, said he had a heart attack before a scheduled address to the Italian Senate on rising anti-Semitism in Europe.

Professor Wistrich was the author or editor of 29 books, including the encyclopedic “Antisemitism: The Longest Hatred.” In that volume he found anti-Semitism’s historic roots in Jewish religious and social exceptionalism, which, he said, antagonized early pagans and rulers who demanded absolute fealty, and which later spread as Christians embraced the divinity of Jesus. He distinguished between classical anti-Zionism, or opposition to a Jewish state, and anti-Semitism, and also between Islam and Islamist terrorism.

But in a letter published posthumously in The Jerusalem Post, he wrote: “The Islamists are the spearhead of current anti-Semitism, aided and abetted by the moral relativism of all-too-many naïve Western liberals.”

Professor Wistrich wrote the text for the Simon Wiesenthal Center’s exhibition “People, Book, Land: The 3,500 Year Relationship of the Jewish People With the Holy Land,” which was displayed at the United Nations headquarters in New York in February and March. The exhibit’s debut in Paris last year was postponed after Arab nations protested that it could undermine Middle East peace talks. It finally opened after “Holy Land” was substituted for “Land of Israel” in the title....