Explanation: In medieval European Christendom, the Jews occupied a strange and uncomfortable place in the policy of the Christian Church. As Jews, the chosen people of YHWH, they were special, the same people and original religion as the primary figure of the Christian faith, Jesus Christ - but as Jews, and not Christians, they were HEATHENS and in need of CONVERSION.

As a 'compromise', rather than simply murdering or expelling them immediately, as with pagans, heretic Christians, or Muslims, they would be magnanimously allowed to exist... but barred from most productive, RESPECTABLE professions! Surely that will pressure them into converting to the TRUE faith!

... when tight-knit Jewish communities passed around the knowledge at the only 'disreputable' labor-and-skill-oriented jobs they were actually allowed to do, Christians would often get furious at the success of nonbelievers working FILTHY, SINFUL JOBS in their midst, and then murder and expel them - and take all their property.