If you mean, being able to read, well, it is very hard to function in modern society if you can't read fluently. As almost all information is in written form. More specifically, well developed reading skills mean you have control over the type of information you take in. You can pick out key ideas etc. Children usually need to be taught reading skills like different ways of reading (eg fiction and non-fiction employ different skills), distinguishing fact from opinion and so on.
