Is love the most significant theme in acts 1–2 of The Merchant of Venice?

Different readers will have a different take on this, but I do not believe that the theme of love is the most significant theme shown in Acts 1 and 2 of Shakespeare's The Merchant of Venice. I think friendship is a more prevalent theme; however, that isn't to say love is excluded as a theme. Bassanio says that he wants to make Portia his wife. That is what is motivating him to seek out Antonio's help. If he wasn't in love, then he wouldn't be seeking help. Presumably, Bassanio is after Portia because of love, but I've always doubted the intensity of that particular love. Bassanio never really sells audiences that he's in love with Portia for reasons other than she is very attractive and quite wealthy. If he marries her, all of his financial troubles go away. Plus, he winds up with an attractive wife. That's not exactly the stuff of pure romance. If Portia were poor and unattractive, I don't believe that Bassanio would be interested at all. That means he's not in love with her. He's in love with what she is and has.

What does Shakespeare convey about different types of love in The Merchant of Venice?

This is a very interesting and complex question and the most interesting and complex relationships in the play for me are the father/daughter relationships.  There are two.  That both fathers love their daughters is a given for me but the expression of the love is not so easy to understand.

First and foremost is the relationship between Portia and her recently deceased father.  Although never physically seen, he looms large in Belmont.  The gilded cage he has placed her in is the root of her wooing in the play.  Dad knew the value of his remarkable daughter.  She is indeed the golden fleece---she is beautiful, brilliant and rich.  The conditions of her wooing are life altering.  If correct, you get Portia; if incorrect, you cannot marry (among other conditions).

We know that Portia and Bassanio are not strangers.  We know that Portia has contempt for the suitors who have already tried in vain.  By the time Bassiano arrives, she knows where her portrait lies and does her best to lead him to the correct choice.

Did Portia avoid her father's "trap" or did he know her well enough to protect her against unworthy suitors and know she would find her match?  That is open to interpretation.  He did love her enough to put a high price on her and in that world, it was a necessary protection.

The relationship between Shylock and Jessica is also complex.  They share only one scene together and Shylock seems strict and unable to show the love he feels for his daughter.  It seem that he has been a single parent in a society where he is a second class citizen and he has had to work hard to provide for her.  That she betrays him is a knife in his heart.  The lose of his jewels and money cannot compare to the pain he feels when he hears that she has traded a ring he got from his dead wife for a monkey.  That he loves Jessica, I do not doubt.  Could he express this love.  No.

Another interesting relationship is the one between Antonio and Bassanio.  Exactly what the relationship is, is up for interpretation. No age is established for Antonio.  If he is an older man, Antonio can be viewed as a surrogate father or lover.  If he is viewed as a young man, the relationship could be that of a best friend or lover.  Antonio is willing to die for his friend, although the bargain is made in a "merry jest" since Antonio has no doubt that he will be able to repay the loan.

As for the young people in the play, there are three different relationships.  The one most likely to succeed is between Portia and Bassanio, although Bassanio is tricked into giving up the ring Portia gave him.  Nerissa and Graziano are another relationship. Nerissa seems rather level headed whereas Graziano seems like a bigot.  As for Jessica and Lorenzo, how can this be a good relationship when it is bassed on theft and deceit?

Many relationships are explored in the play, but the various relationships concerning love are layered and complex and above all revealing.

What does Shakespeare convey about different types of love in The Merchant of Venice?

Shakespeare offers three different versions of what we might consider romantic love--Portia and Bassanio, Jessica and Lorenzo, and Nerissa and Gratiano.  The primary couple, Portia and Bassanio, represent what Shakespeare normally portrays as true love.  Portia is willing to sacrifice for Bassanio and goes to great lengths to do so. Their relationship involves wit and banter much like the primary relationships of Shakespeare's comedies (As You Like It, Much Ado about Nothing, etc.).

Jessica and Lorenzo possess the impulsive love of a young couple.  They are similar to Romeo and Juliet, especially in Jessica's disappointing her father.  While many would view them as a romantic couple, it is obvious that after their elopement, they do not truly know much about one another and that they share very different views of life (hence, their discussion about music). Their relationship seems to be more of a warning from the playwright that impulsivity and youth do not make for a successful marriage.

Nerissa and Gratiano certainly provide comic relief but also illustrate a relationship based on lust.  While this is not love, Shakespeare includes them to show how different their relationship is from the others'.

In regards to familial and brotherly love, Antonio and Shylock illustrate the effects of possessing it and of possessing no love at all. Antonio is such a loyal friend to Bassanio that he loans him money once again.  He wants to see his friend happy and is willing to risk his life to help Bassanio.  In the end, even though he ends up with his life and his friend's life spared, he is still not happy and perhaps has realized that love between friends is not enough.  In contrast, Shylock shows what it is like when one does not love or feel loved at all. When Shylock's daughter elopes, he is not concerned about losing her or about her safety; instead, he rants about his lost jewels. Similarly, after Act 4's trial scene, Shylock ends up with nothing.  His daughter is gone for good; his business is gone, and he has been humiliated in front of all of Venice. Shakespeare seems to use him to teach that all the riches in the world are worth nothing, for if one loses his wealth and has no friends or family, he is completely ruined.

What does The Merchant of Venice teach about love?

One thing we might learn about love from Shakespeare's play is that there are many differenty levels to the act of love. First, there is Shylock who at first appears to love his daughter. However, when she shames him by running away with a Christian, Shylock's love for Jessica is quickly stripped away, even more so when he discovers that she has taken his money with him. At this point, readers might question which Shylock loves more: his daughter or his money.

Bassanio's love is also rather shallow. He claims love for Antonio, but one wonders if this too is based on money. After all, Antonio lends Bassanio money whenever he asks for it. Bassanio's initial attraction to Portia is also based on money. Whether he overcomes this is not quite clear, as Bassanio's commitment to his love of her comes in question when he gives away the ring that Portia has given him.

Portia's love goes a bit deeper. First, she goes to a lot of trouble to save Antonio, based merely on Bassanio's friendship for Antonio. Then Portia forgives Bassanio's transgression over the ring, despite the fact that he failed her test of his love.

However, the deepest love portrayed might be that of Portia's father, who even in death made arrangements to find the most worthy of suitors for his daughter. Whether the king's plan succeeded or failed is immaterial. His love for his daughter was so important, he created a plan that he thought would work.

What does The Merchant of Venice teach about love?

Well, there's what Shakespeare shows about love, and there's what we learn from it. You might learn something very different, and you'll want to reflect on what he shows us.
That said, I'll gladly share a few thoughts about what Shakespeare shows us about love in this play.
First of all, he shows us that love is interwoven with other drives and desires. (Think of Bassanio's desire to marry Portia in part for her money.)
Second, Shakespeare shows us that there is an element of randomness to love, and that it is in part a game. (Think of the challenge of the caskets.)
Third, Shakespeare shows us that love carries risk. (This would be the whole "pound of flesh" deal.)
Finally, Shakespeare shows us that true love survives through all tests and trials, and finds a way.
Greg