JERUSALEM—Isaac Herzog, scion of a prominent Zionist family, took the oath of office on Wednesday and became Israel’s new president. With one hand on a Bible before the Knesset—Israel’s parliament—Herzog, 60, assumed the largely ceremonial position that is designed to forge national unity and serve as the country’s moral compass. The parliament chamber was festooned with large bouquets of white lilies for the inauguration. Military rabbis blew rams’ horns, followed by a performance by a children’s choir. Herzog, whose father, Chaim, served as Israel’s president in the 1980s, succeeded Reuven Rivlin as Israel’s 11th president and is to hold office for a single seven-year term. Chaim Herzog also served as Israel’s ambassador to the United Nations. The new president’s pedigree includes his grandfather, Yitzhak HaLevi Herzog, who was the country’s first chief rabbi. His uncle, Abba Eban, served as foreign minister and ambassador to the UN and United States. “The …