a. Just Mercy is an autobiography, where the author, Bryan Stevenson, shares his memoirs.
b. To Kill a Mockingbird greatly influenced Stevenson as a lawyer. Indeed, while he obviously admires Atticus Finch ("bravely"), he nonetheless points out the white lawyer's failure to save the innocent black man ("not successfully defended"). He seems to be disgusted with the Americans' failure to learn Lee's (the author) messages about racial violence and presumption of innocence. He denounced the persistence of racial violence over time ("its harder truth did not take roots"). The "modern" Atticus would successfully defend Black Americans.
c. The scene takes place in a courtroom during Walter McMillian's new trial vs The State (l.23-24) after he had been convicted of capital murder and sentenced to death (l.26). Stevenson is making his opening statement to discredit the witness, Myers, in the hope of clearing McMillian of all the charges brought against him.
d. He argued that the testimony of Ralph Myers was completely false.
e. He implicitly compares himself to Atticus Finch with one difference: he wants to be successful (1st excerpt).
In the second excerpt, he also wants to convince the judge and promote racial justice = Atticus and Stevenson are two lawyers fighting the unfairness of America's justice system.