* It's a grave act: He says "killing a mockingbird is a sin" because mockingbirds are innocent and harmless creatures who only bring joy. This parallels his belief that taking an innocent life is a grave moral offense.
* Justice vs. Revenge: Atticus distinguishes between the legal act of executing a condemned criminal and the act of taking a life out of revenge or hatred. He argues that killing in anger or without a clear reason is wrong.
* Respect for life: Atticus emphasizes the importance of valuing all life. He defends Tom Robinson, a black man falsely accused of assault, because he believes everyone deserves a fair trial and a chance at justice.
* Consequences for the killer: Atticus believes that taking a life, even in self-defense, leaves a lasting stain on the killer's soul. He emphasizes that even in dire situations, there are often other options.
While Atticus doesn't explicitly call killing a sin, his philosophy aligns with many religious and moral beliefs that consider taking a life a serious transgression. He teaches his children and readers to respect life, seek justice, and avoid unnecessary violence.
It's important to note that "To Kill a Mockingbird" is a novel, not a theological treatise. Atticus's perspective on killing is a reflection of his own moral compass, not necessarily a universal definition of sin.