I think that the primary significance of Assef's complete targeting of Hassan in the first confrontation is to bring out how the Hazara are viewed in the Afghanistan of the time period. There is a social stratification where the Hazara are socially viewed as outcasts. The lack of stable and strong leadership that would remove such a perception is evident in how Assef boasts about the new leadership in Afghanistan and how he wishes that the same racial purification policies of Hitler would be pursued by this new leadership. The ethnic cleansing that becomes such an integral part of Afghanistan's tragic history is evident in this confrontation. The targeting of Hassan is something that is used to show how the nation of Afghanistan itself will devolve into targeting specific people in order to prop up the status of others. It is also a good foreshadowing element to show how Assef will rise to a position of significance in the Taliban government, an order that makes it clear that the policies of targeting and scapegoating enable its own success to be evident. In bringing out this element to the narrative early on and with Assef, the groundwork is laid for how this will become significant later on in the novel's development.