Quote 1
NERISSA
Your father was ever virtuous, and holy men
at their death have good inspirations. Therefore the
lottery, that he hath devised in these three chests of
gold, silver and lead, whereof who chooses his
meaning chooses you, will no doubt never be
chosen by any rightly but one who shall rightly
love. (1.2.27-33)
Nerissa insists that Portia's father had good intentions when he devised the casket contest as a way to determine Portia's husband. (Whoever picks the correct casket gets Portia and all of her dead dad's money.) Yet we can also read the casket contest as a way for Portia's dad to control where his wealth goes. By orchestrating his daughter's marriage from beyond the grave, Portia's father is able to transmit all of his wealth to the man of his choosing, which is why Portia complains that she is a "living daughter curbed by the will / of a dead father" (1.2.3).
Quote 2
NERISSA
You need not fear, lady, the having any of
these lords. They have acquainted me with their
determinations, which is indeed to return to their
home and to trouble you with no more suit, unless
you may be won by some other sort than your
father's imposition depending on the caskets. (1.2.100-105)
The casket contest for Portia's hand in marriage is a pretty risky undertaking: if a suitor chooses the wrong casket, he can never pursue marriage (with anybody) again. Here we learn that some of the suitors would rather not play this game. They clearly desired marriage (or they wouldn't have shown up), but it isn't worth the risk. This pretty much automatically disqualifies them from being worthy of marrying Portia. It seems her father was looking for someone who'd be willing to risk everything for the girl.
Quote 3
NERISSA
The ancient saying is no heresy:
Hanging and wiving goes by destiny. (2.9.88-89)
Here Nerissa is commenting on the precariousness of the marriage lottery that Portia's father has arranged. But still—we don't know about you, but when we hear anyone compare "wiving" (courtship) to "hanging," we get a little nervous.