This exchange, occurring in the brief space between Monygham asking for help
and relating his "scheme" to deceive Sotillo, involves the difference
between false hope and true hope, the latter represented by the treasure. Nostromo,
representing the innocent People, cannot imagine restoring society on the basis
of anything but true hope, i.e, the "treasure." On the surface he
is saying that he won't reveal his hoard (in an extreme way that evokes
his growing slavery to it), but on the deeper level the line means that the
People can't place their hope again in society, not as represented by
the likes of Sotillo, Pedrito and Gamacho. The reason they can't is precisely
because of what they now know: that there is no hope in societal relations,
that they are exploitative, destructive and illusory, that all men are
essentially men of "destructive rapacity." In Nostromo's remark we
again find the symbolic notion of bringing the silver back ashore (i.e., restoring
faith in social structures and crusading ideals), and it is again presented
as being physically impossible.
Monygham, who has not yet related his scheme, agrees completely with Nostromo.
His belief that the silver is irretrievably lost corresponds to the cynical
conviction -- worthy of the Devil -- that no true hope is possible to
mankind. It is the Devil's belief (and his limitation) that mankind's only fate
is to be manipulated by false hope. In this sense Nostromo's secret knowledge
of the silver on the Great Isabel corresponds symbolically to the People concealing
what the Devil does not suspect: the incorruptible integrity of their character,
which is the true hope and mankind's true value.