what is the message the prince of arragon got?

The scroll in the silver casket reads, "There be fools alive, I wis {know} / Silver o'er; and so was this." Portia reminds him that no man is permitted to judge his own cause. When he opens the silver casket, he finds within "the portrait of a blinking idiot" - a picture of a fool's head. He protests the contents; he chose according to what he felt that he deserved.