What three things will Shylock do with a Christian?
In Shakespeare's "The Merchant of Venice," Shylock lays out his conflicted feelings about Christians when Bassanio asks Shylock for a loan of 3,000 ducats. Bassanio wants to borrow the money from Shylock, with Antonio's wealth backing Bassanio up. Shylock seems willing to make the investment, but wants to talk with Antonio first. Bassanio invites Shylock to dine with him and Antonio so they can discuss the agreement, but Shylock is repulsed, saying,
"Yes, to smell pork; to eat of the habitation which
your prophet the Nazarite conjured the devil into. I
will buy with you, sell with you, talk with you,
walk with you, and so following, but I will not eat
with you, drink with you, nor pray with you" (1.3.34-38).
So Shylock is perfectly willing to do business with Christians—in fact he doesn't have much of a choice, as a money lender in Venice at the time Shakespeare wrote the play. He relies on the Christian majority and their loans to keep his business going. He also says he will walk and talk with Christians without (much) complaint.
Where Shylock draws the line is at eating, drinking, and praying with Christians. He indicates why at the beginning of the above quote. Jews like Shylock keep kosher—they follow the Torah's rules for clean and unclean foods and ways of storing and preparing them. Christians do not follow these same rules. Shylock predicts that dining with Bassanio and Antonio will mean a dinner that is not kosher—including pork (pigs are one of the animals God forbade people from eating in the Torah—Lev. 11:3; Deut. 14:6).
It's not just the social awkwardness of avoiding foods that keeps Shylock from eating, drinking, or praying with Christians, though. This quote gets at the fundamental differences between Jews and Christians that Shylock seems to think—at least at this point in the play—are insurmountable. The Christians of the story are just too different for them to have any personal connections with one another to to build a diverse community with. Even though the setting of Venice in Shakespeare time was a hub of trade with numerous nationalities, religions, and cultures, Shylock's comment suggests that it was not a melting pot where everyone got along. He is unwilling to engage in anything but the most surface-level interactions with Christians. Judging from most of the Christian characters' casual Antisemitism, the feeling is mutual.