how does bassanio prove his citing the examples of law and religion?

Bassanio says that true beauty does not lie in wealth. Wealth looks nice on the surface but is empty underneath hence he rejects the gold casket,

So many outward shows be least themselves: The world is still deceived with ornament. In law, what plea so tainted and corrupt, but, being seasoned with a gracious voice, obscures the show of evil?