Judaism and Christianity are religions bound together by their claims to the same biblical covenant initiated by God with Abraham and his descendants. Yet, despite the inseparable connection between the election of Israel and that of the church, between the "old" and the "new" covenant, this shared spiritual patrimony has been the source of a type of violent sibling rivalry competing for the same paternal love and inherited entitlement. God, it seemed, had but one blessing to bestow. It could be given to either Jacob or Esau--but not both. In the twenty-first century, however, Jews and...