In Act I scene 2 Nerissa makes explicit the reason why Portia's father devised such a strange way of selecting posthumously the suitor who will marry his daughter. Because he was such a "virtuous" and "holy" man, the lottery will only be solved by a man who is able to be "rightly loved" by Portia, because he will display sufficient wisdom, intelligence and humility in selecting the right casket as to make him a good partner for Portia. This is something that Bassanio achieves in Act III scene 2, when he correctly chooses the lead casket and reads the following scroll left by Portia's father:
You that choose not by the view
Chance as fair, and choose as true:
Since this fortune falls to you,
Be content, and seek no new.
The test of the caskets thus discerns whether the suitor is swayed by outward appearances and impressions of wealth, as hinted at by the gold and silver caskets, or whether they are able to "choose not by the view" and select an apparently worthless substance that holds great wealth inside. Because Portia is "richly left," her father wanted to protect her from being the prey of fortune seekers who would only be after her money. Bassanio arguably shows that he is not after money through his willingness to select the worthless lead casket, showing himself to be a true suitor.