And I will bless those who bless you [who confer prosperity or happiness upon you] and curse him who curses or uses insolent language toward you; in you shall all the families and kindred of the earth be blessed – by you they shall bless themselves. [Amplified Bible].
To look with disfavor on the Jews was to invite God’s displeasure; to treat the Jews offensively was to incur His wrath.
But to befriend the Jews was to bring down upon one’s head the rewards of a promise that could not be broken.
– The Amplified Bible: page 14