The lead casket read:
"Who chooseth me must give and hazard all he hath".
It is indeed true that Bassanio was not swayed by the outer appearance of gold or silver and the captions that they read. Taking into consideration the fact that Lady Portia's father was a virtuous man and as Nerissa said in ACT I SCENE II:
" Your father was ever virtuous, and holy men at their death have good inspirations..."
we are obliged to think that Lady Portia's father must have had thought of a watertight plan so as to give his daughter and wealth to a deserving suitor. In my opinion the caption on the lead casket itself says the needful.
"Who chooseth me must give and hazard all he hath".
Whoever seeks true love must give and should not expect anything in return and should be ready to take all the risks for his beloved. That is the reason, in my view, that prompted Lady Portia's father to devise such a caption for base lead. Morocco mocked at it by saying in ACT II SCENE VII:
"Must give for what? For lead, hazard for lead?"
He was swayed by appearance and lead by lust in choosing gold. Bassanio on the other hand was not swayed by appearance and he chose the right casket.