I think that Arthur (Boo) Radley showed passion at the very end of the book when he saved the Finch children from the vengeful Bob Ewell.
Atticus and Heck Tate showed passion when they made the decision not to bring Arthur Radley out into the public eye as the town hero even though he deserved the honor.
Atticus showed the greatest passion and love of his fellow man in defending Tom Robinson in court. He stood on his values against overwhelming odds in his hometown. "Greater love, has no man, than he would lay down his life for his friends." (John 15:13) Atticus laid his career on the line in defense of Tom Robinson. He sat at the jail house at night knowing that a lynch mob would show up, yet he stayed right there.
Scout showed courage when she confronted the entire lynch mob by the recognition of one of her classmate's fathers. After a brief conversation, the lynch mob dispersed. Scout loved her father and knew that something bad was about to happen, and she had to do something about it. She showed genuine kindness and neighborly love when she walked Boo Radley home after the heroic scene of saving the children's lives.