The following line is taken from Act 1, Scene 3, of William Shakespeare's The Merchant of Venice): "to eat of the habitation which your / prophet, the Nazarite, conjured the devil into!" As part of this conversation, Shylock is refusing to dine with Bassanio and Antonio.
The quote in question is an analogy to the Bible. In Matthew 8: 30-32, Jesus drives demons out of two man into a herd of pigs. The relevance of this plays into Shylock's refusal, a one of Jewish descent, to eat pork. Jewish people refuse to eat pork because do not believe the animal to be kosher (only animals with split hooves and that chew their cud are considered kosher).
Essentially, by referring to the "demonic" pigs, Shylock is compounding his dislike and disapproval of those who eat pig. Antonio and Bassanio are not Jewish and both eat pig/swine.