Please explain your understanding of the quote and then explain to which theme the quote relates in The Old Man and the Sea."he was too simple to...

This passage is from the exposition of Ernest Hemingway's
The Old Man and the Sea.  As the novella opens, Santiago has had no
luck fishing in eighty-four days. His friend, the boy, has been told by his father to
fish with others who are more fortunate.  And, the other fishermen ridicule him, but he
is not angry.  Still others, the older fishermen glance and him and become melancholic,
but they dissemble and speak politely about the currents and depths to which they have
drifted their lines. 

When the boy offers to bring Santiago
two sardines for bait, the "old man" agrees without
protest. 

He
was too simple to wonder when he had attained humility.  But he knew he had attained it
and he knew it was not disgraceful and it carried no loss of true
pride.

He tells the boy that
tomorrow will be a good day.  Santiago says this more, however, for the boy's sake than
for his own.  For, now that he is older, Santiago does not always care so much about
himself.  He does not argue over things anymore, either.  Indeed, these lines pertain to
the theme of Youth and Old Age."  For, when he was young, Santiago would not have been
so quiet about having no fish for so long.  The boys' deference to him also touches upon
the social concern of the notion of respect and concern for the aged, and the loneliness
of old age.