Why do Atticus' eyes fill with tears when he sees the food offerings from the African American community?

The African American community experienced something miraculous when they witnessed Atticus defend a black man to the best of his ability.  That was why they all stood up for him in the courtroom when he passed under the balcony where they were sitting.  They knew that no other lawyer would have defended a black man like Atticus did.  He prepared a logical defense that should have set Tom free, and in a just court system,...

The African American community experienced something miraculous when they witnessed Atticus defend a black man to the best of his ability.  That was why they all stood up for him in the courtroom when he passed under the balcony where they were sitting.  They knew that no other lawyer would have defended a black man like Atticus did.  He prepared a logical defense that should have set Tom free, and in a just court system, Tom would have been found innocent.  Unfortunately, the jury condemned Tom to prison simply because he was a black man.  This was something the black community would have been used to; the justice system of the South often convicted black men without a fair trial. 

Atticus cried because he was not only touched by the respect they showed him, but because he also knew that it was probably a hardship for them to bring him food.  The rural black community was very poor in Maycomb, and their offering of food to Atticus showed their thankfulness and their respect for the one white man who defended Tom with integrity and honesty.