In the second chapter of Harper Lee's To Kill a Mockingbird, when Scout surprises her first-grade teacher by already knowing how to read, we learn that Scout can't really remember a time when she couldn't read. She also says that her father Atticus never taught her.
As Scout explains, reading is something that just came naturally to her. She curls up in his lap at night when he comes home from work and looks at anything he is reading. She's not sure "when the lines above Atticus's moving finger separated into words," but they certainly did; plus, she has no memory of a time when they weren't words for her. Hence, Scout developed an early ability to read because she is precocious and because reading became a time for her to bond with her father.
Most importantly, she explains to her reader, "Until I feared I would lose it, I never loved to read. One does not love breathing." In other words, Scout is saying that she never realized how much she loved to read until her teacher, Miss Fisher, told her to stop reading. She didn't realize it because it was as much a part of her every day existence as breathing. Hence, for Scout, reading is as valuable to her as breathing, especially because it is a method for her to bond with her father.