Quote 1
LANCELET
Nay, indeed, if you had your eyes, you might
fail of the knowing me. It is a wise father that
knows his own child. (2.2.73-75)
Lancelot never makes clear that he loves his father, but teases him instead. (And teases pretty cruelly, joking that Old Gobbo's son is dead.) It seems Lancelot takes advantage of his father's blindness and the fact that he doesn't really know him. This is a seemingly silly aside, but it's actually an interesting parallel to the relationship between Jessica and Shylock. We're never really clear on whether they love each other, but it is clear that Shylock doesn't really know who Jessica is. Jessica, like Lancelot, betrays her father, but while Lancelot does it in jest, Jessica's betrayal is much graver and seriously calls her love and loyalty into question.
Quote 2
LANCELET
There will come a Christian by
Will be worth a Jewess' eye. (2.5.43-44)
Not even love can surmount religious restrictions. Though Lorenzo and Jessica may be bound together in love, they're still defined and separated by their religious identities.
Quote 3
LANCELOT
"Budge," says the fiend. "Budge not," says my conscience.
"Conscience," say I, you counsel well." "Fiend," say I, "you
counsel well." To be rul'd by my conscience, I should stay with
the Jew my master, who—God bless the mark!—is a kind of devil;
and, to run away from the Jew, I should be ruled by the fiend,
who—saving your reverence!—is the devil himself. Certainly the Jew is the very devil incarnation; and, in my conscience, my
conscience is but a kind of hard conscience to offer to counsel
me to stay with the Jew. The fiend gives the more friendly
counsel. I will run, fiend; my heels are at your commandment; I
will run. (2.2.1)
There's no evidence that Shylock is particularly awful to Lancelot—it seems that religious attitudes are at work in painting Shylock as the devil incarnate. He's caught between a rock and a hard place, as often happens in the play. Lancelot gives no reason for his choice; he just dismisses his conscience as a hard one, giving worse advice than the fiend.
This is particularly interesting when we think of the other person who must choose between Shylock and something else: Jessica. Though we never really see her reasoning, maybe Shakespeare is suggesting it was something similar to this?