Within the novel one motif occurs much more than others, it is the fact that it's a "sin to kill a mockingbird". This is another way of saying that the destruction of innocence is wrong. Many characters from the text are symbolized by mockingbirds; they are innocent characters who were harmed. Tom Robinson is a perfect example, and in fact a newspaper compares his death to "the slaughter of songbirds". Could this be a coincidence? During his trial Tom is wrongly convicted and sentenced to death, yet he was an innocent man. This is a form of the destruction of innocence.
This motif mainly assists the theme of good vs. evil.