BASSANIO In Belmont there is a lady richly left, [...] And many Jasons come in quest of her. (1.1.168, 179)
As we see here, Bassanio is interested in courting Portia because her father has left her a ton of dough. This would be great for Bassanio, who's completely broke. What's also interesting is the fact that Bassanio refers to Portia's suitors as a bunch of "Jasons" in "quest" of the Golden Fleece. (In Greek mythology, Jason and the Argonauts went after the golden fleece of a winged ram, which landed Jason the throne of Iolcus.) Bassanio's reference to the Greek myth turns his courtship of Portia into an exciting and lucrative conquest.
BASSANIO Her name is Portia, nothing undervalued To Cato's daughter, Brutus' Portia. (1.1.172-173)
This doesn't bode well as a comparison: Brutus' Portia was indeed a noble woman, but Brutus wasn't exactly the greatest husband. In Shakespeare's play Julius Caesar, Portia dies a fairly arbitrary death, and Brutus shakes it off pretty easily. Hmm.
ANTONIO Try what my credit can in Venice do; That shall be racked even to the uttermost To furnish thee to Belmont, to fair Portia. Go presently inquire, and so will I, Where money is, and I no question make To have it of my trust, or for my sake. (1.1.187-192)
When Antonio gives Bassanio the financial assistance he needs to woo Portia in style, Portia becomes the medium through which Antonio can strengthen his relationship with Bassanio. Since Bassanio will be further indebted to Antonio, the two friends will become that much closer and Bassanio will reap the financial rewards of being married to Portia. In other words, marriage is less about the relationship between husband and wife than it is an opportunity for Antonio and Bassanio to strengthen their bonds.
Act 1, Scene 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.
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).
Act 2, Scene 1
PORTIA You must take your chance, And either not attempt to choose at all Or swear before you choose, if you choose wrong Never to speak to lady afterward In way of marriage. Therefore be advised. (2.1.40-44)
It seems rather arbitrary and harsh that the condition to try for Portia's hand is that losers can never seek marriage... ever again. Still, it holds up marriage as a really serious affair and helps separate the men from the boys in terms of who's really willing to sacrifice for the chance to marry Portia.
Act 2, Scene 3
Alack, what heinous sin is it in me To be ashamed to be my father's child? But though I am a daughter to his blood, I am not to his manners. O Lorenzo, If thou keep promise, I shall end this strife, Become a Christian and thy loving wife. (2.3.16-21)
Jessica can't wait to elope with Lorenzo, but why? As literary critic Janet Adelman points out in Blood Relations, "marriage appears to occur to her largely as a way to escape" from being her father's daughter (71). Later, when Jessica declares "I shall be saved by my husband. He hath made me a Christian" (3.5.3), we can see that Jessica really is ashamed of being the Jewish daughter of Shylock. Check out "Race" quote #9 for more on this.
Act 2, Scene 6
LORENZO Beshrew me but I love her heartily, For she is wise, if I can judge of her, And fair she is, if that mine eyes be true, And true she is, as she hath proved herself. And therefore, like herself, wise, fair and true, Shall she be placèd in my constant soul. (2.6.54-59)
From the looks of this passage, Lorenzo seems to genuinely love Jessica, who is in the process of running off to marry him. Still, we can't help but notice that the marriage is a lucrative hookup for Lorenzo. When Jessica sneaks out of her dad's house, she steals a bunch of gold and says, "I will make fast the doors and gild myself / With some more ducats" (2.6.5). So even if Lorenzo doesn't just marry Jessica for her money, the play certainly makes her out to be, like Portia, a meal ticket.
Act 2, Scene 9
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.
Act 3, Scene 2
PORTIA Happiest of all is that her gentle spirit Commits itself to yours to be directed As from her lord, her governor, her king. Myself, and what is mine, to you and yours Is now converted. But now I was the lord Of this fair mansion, master of my servants, Queen o'er myself; and even now, but now, This house, these servants, and this same myself Are yours, my lord's. I give them with this ring, [handing him a ring.] Which when you part from, lose, or give away, Let it presage the ruin of your love, And be my vantage to exclaim on you. (3.2.167-178)
According to Portia, marriage is about a woman giving over herself (and all her money and property) to a partner. This is what she does here when she gives Bassanio "this house, these servants" and a ring. (In the 16th century, when a man married a woman, she automatically became his property and legal responsibility.)
At the same time, Portia is also being pretty crafty here. Because she gives him more than he can possibly give her in return, Portia binds Bassanio to her. Check out what we have to say about Portia's ring in "Symbolism, Imagery, Allegory" for more on this.
PORTIA First go with me to church and call me wife, And then away to Venice to your friend! For never shall you lie by Portia's side With an unquiet soul. (3.2.316-319)
Portia's a clever girl. She knows Bassanio is going to leave her to help his BFF, but she insists that they get hitched first. This way she seals Bassanio to her. When he goes to Antonio, he'll go as her husband, not merely as Antonio's friend.
Graziano (a.k.a. Gratiano)
GRATIANO My Lord Bassanio, and my gentle lady, I wish you all the joy that you can wish, For I am sure you can wish none from me. And, when your honours mean to solemnize The bargain of your faith, I do beseech you Even at that time I may be married too. (3.2.193-198)
Graziano's marriage to Nerissa is a calculating, unornamented version of the institution that is actually a neat parallel to Bassanio and Portia's hookup. Graziano says as much when he declares that he and Bassanio are the "Jasons" who have "won the fleece" (3.2.6).