How does the idea of guilt play into Rahim Kahn's strategy to get Amir to go and look for Sorab in The Kite Runner?

Guilt and redemption are two of the primary themes of this
novel, and Rahim uses Amir's guilt over his abandonment of Hassan during the attack and
his subsequent treatment of Hassan shortly after that to pull him back to Afghanistan to
search for Hassan's son, Sorab.  Amir, as a first person narrator, has revealed to us
from the first page of the novel that he feels guilty about what he did to Hassan back
in their youth, and it is has all haunted him through to his adulthood.  When Rahim
calls to tell him about Hassan's death and the plight of his son Sorab, the past has
"caught up" with the present of Amir's life.  Though Rahim doesn't state anything
directly, he makes it rather implicitly clear that he knows
all that happened back on the day of the kite running contest and
what Amir did to drive Hassan and his father from Amir and Baba's home.  He also reveals
that Hassan was Amir's half-brother, and therefore, Sorab, is Amir's half-nephew.  Amir
always sensed an unusual closeness between Baba and Hassan and his father, but this
explains everything better.  Amir is absolutely compelled to do what he can to do right
by the memory of Hassan, to show loyalty to blood relations, and to right the wrongs of
his past and achieve some measure of personal redemption and relief from the guilt he
has carried around all these years.  It is a wonderful irony that when he does find
Sorab, Amir must fight the attacking bully of their past -- Assef, in order to secure
Sorab's life.  His physical fight with Assef is kind of the fight he should have had
back when they were all boys.  It is also a great irony that Sorab is the one to finally
take down Assef with the use of sling-shot -- a weapon he learned to use from the master
-- his father, Hassan.