The role of wealth and friendship are evident in the character of Antonio. It would seem that he is very rich, although his money is tied up in his most recent shipping venture. It is also his friendship with Bassanio that eventually leads him into danger.
Despite the fact that Bassanio comes from a good family, they are no longer wealthy. In order for him to be able to woo Portia, he must at least appear to have money. He is forced to ask his friend Antonio for the money.
Since Shakespeare doesn't tell us how old Antonio is, exactly what their relationship is up to interpretation. If he is an older man, their relationship could be like a father/son relationship. If he is the same age, a homosexual relationship can be implied. There are a number of possibilities.
Whatever their relationship is, the money is a huge sum and Antonio agrees to help his friend.