what is the significance of the casket scene...?

In The Merchant of Venice, Shakespeare presents two literal, but vastly different, trials. However, it is the casket trial in Belmont, which is perhaps the most interesting. Unlike the legal trial in Venice, the trial of the caskets is fanciful and fairytale-like.

In Belmont, Portia’s suitors are presented with three caskets made of gold, silver and lead. Each man is asked to choose a casket, if he chooses the one with a portrait of Portia inside, he will win her hand in marriage. Each casket has a riddle, which, if deciphered correctly, tells of the contents. This trial, designed by Portia’s father, allows him to screen his daughter’s suitors in absentia.

Check out details on each casket (and significance) at the following link.