For You A Thousand Times Over

There is
also a class and ethic dynamic in  that I believe is reflected in the use
of this statement, first by Hassan to Amir and then later by Amir to Sohrab.  Amir and Hassan
are not from the same class or ethnic group, and this difference is central to the plot and
themes.  

Amir is a Pashtun, and Hassan is a Hazara.  The Pashtuns are the
ruling class in Afghanistan, and it is clear that the Hazaras are a lower class and ethic group,
historically treated quite poorly, and also shown as treated quite poorly in the setting of the
novel. Hassan and his father Ali are servants in the household of Baba and Amir, and while Amir
and Hassan are raised together, there is a clear line in Amir's mind of their differences.  Amir
notes,

But in none of his stories did Baba ever refer to
Ali as his friend. ... I never thought of Hassan and me as friends either (25).

Amir looks down upon Hassan, and the relationship is such that
Hassan saying "For you, a thousand times over" is really what Amir expects from
Hassan, because he perceives him to be an inferior servant.  He really does not see that Hassan
is a true friend and is saying this out of love, not out of duty as a servant.  

On his long journey of learning and repentance, as Amir finds himself and his father
looked down upon in the new land, the shoe is on the other foot. They are subject to small,
daily humiliations in the United States, for example, Baba's humiliation at collecting any kind
of benefits and Amir's concern about not being quite good enough to wed Soraya, whose father is
a general. Amir begins to understand what it feels like to be regarded as inferior.  By the time
he rescues Sohrab and says to him, "For you, a thousand times over," this is meant to
represent not only his repentance for what he had done to Sohrab's father, but also his
understanding that we must all be servants to one another and that class and ethnicity should
play no part in our willingness to do so. He is saying this out of love and friendship, as
Hassan had said it to him. 

So, while there is no question that the use of
this declaration represents Amir's repentance for all he has done wrong to Hassan (and Ali), I
do think that the class and ethnic tension are part of the meaning behind its use,
too.