Paul “did all of this because he was heading off a primitive seed form of antisemitism—believing Gentiles vaunting themselves over against unbelieving Jews. But his command is explicit: ‘Boast not against the branches’ (v. 18). ‘Be not high-minded but fear’ (v. 20). Antisemitism is therefore nothing less than disobedience to an express apostolic command.”
American Milk and Honey, p. 142