clash of those ideals with the reality of your father's fault?

"Well, there's this to think of now, Derry, now that you are a
man--that life isn't white and black, it isn't sheep and goats--it
isn't just good people and bad people with a great wall between. Life
is gray and amethyst, it is a touch of dinginess on the fleece of the
whole flock, and the men and women whom you meet will be those whose
great faults are balanced by great virtues and whose little meannesses
are contradicted by unexpected generosities.

"I am putting it this way because I want you to realize that except for
the one fault which has shadowed your father's life, there is no flaw
in him. Other men have gone through the world apparently untouched by
any temptation, but their families could tell you the story of a
thousand tyrannies, their clerks could tell you of selfishness and
hardness, their churches and benevolent societies could tell you of
their lack of charity. Oh, there are plenty of good men in the world,
Derry, strong and fine and big, I want you to believe that always, but
I want you to believe, too, that there are men who struggle continually
with temptation and seem to fail, but they fight with an enemy so
formidable that I, who have seen the struggle, have shut my
eyes--afraid to look--.

"And now I shall go back to the very beginning, and tell you how it all
happened. Your father was only a boy when the Civil War broke out. He
came down from Massachusetts with a regiment which had in it the blood
of the farmers who fired the shot heard round the world--. He felt
that he was fighting for Freedom--he had all of your ideals, Derry;
plus, perhaps, a few of his own.