Harper Lee's novel To Kill a Mockingbird was written in 1960, at the point in which the Civil Rights Movement was gaining attention. In her narrative, Lee portrays the prevailing racism in the Jim Crow South with her character of Atticus Finch embodying the courage to face this racism and do what is right. Employing the character of Atticus, Harper Lee puts forth a new message for the Deep South: one of tolerance. Atticus Finch faces the censure of his town, but brings his courage to the courtroom and defends Tom Robinson who has been accused of raping a white girl.
Such characters as Bob Ewell and Mr. Cunningham, two uneducated and poor men, are unable to break the chain of biases that have haunted their environment. Ewell attempts to defend his sordid life by throwing blame upon a one-armed Negroe, and while Mr. Cunningham would like to vote for acquittal for Tom, he acquiesces to majority rule. With others in the community, the conventional wisdom of the era exerts an influence that the uneducated cannot overcome. Instead they repeat phrases that rationalize their behavior such as
that all Negroes lie, that all Negroes are basically immoral beings, that all Negroes are not to be trusted around women.
or the comments of such as Mrs. Merriweather who complains,
"I tell you there are some good but misguided people in this town...Folks in this town who think they're doing right, I mean....but some of 'em in this town thought they were doing the right thing a while back, [the Civil Rights Movement begun in 1955] but all they did was stir 'em up. That's all they did."
By illustrating that inexperience and ignorance parallel an inability or refusal to change, Harper Lee brings to light what she perceives as one of the ills of American society, the existence of castes.
When you reference inexperience in your question, I believe you refer to Scout as a young child having yet experienced much of the world, or Dill when he has trouble understanding the racism during the trial, or Mayella as she failed to ever encounter a serious relationship with a man or even a friend. When you refer to ignorance, I think you cite instances in the story when a character just doesn't know any better. This could be the women at the missionary circle, or Bob Ewell, who was a third generation recipient of welfare.
I think Harper Lee parallels the two because they both have similar results for both the individual and society at large. She is demonstrating that society could help educate those who don't know any better. She is also proving that those who don't experience more adult circumstances are certainly at a disadvantage when trying to participate in the adult world. Thus, there lies within each of us a social responsibility to help bridge the gap either through education or helping foster understanding.
She uses a specific era when both ignorance and inexperience ran rampant throughout society. The Jim Crow laws were instated not out of experience, but ignorance. Instead of trying to overcome a problem, it was made worse. This is part of what Atticus was fighting for with Tom Robinson's trial. Racism did, as a result of Tom's trial, become worse for a little bit. It stirred the anger of white folks against blacks, but the white folks weren't educated with the facts until Atticus brought them to light so cleverly in the trial.
Change is possible in societies, but not when inexperience and ignorance rule. Change occurs when people are openminded, I believe Harper Lee set out to prove this is a need in America. Thus, her work has become likely the most difinitive of American Literature.