Imagine a world where knowledge is imparted through books, but no one is able to read. It is a depressing image that conveys no hope for future generations. That is the driving factor behind the societal pressure to read. Sadly, there are still people in our society who never learned to read. These people are echoes of what humanity used to be during the times when only high-ranking church officials and aristocracy were allowed to learn. Nowadays, in modern society, it is impossible to even imagine a world where one has to be "allowed" to learn something as simple as reading.
By learning how to read, a person will be able to transfer his knowledge onto future generations. Reading is fundamental to acquiring knowledge and sharing this knowledge with others. If an entire generation didn't learn to read or write, the effects of this would be devastating. Reading is how humanity passes on knowledge to others; without it, transmission of knowledge would not be easy.
As a person develops into a proficient reader, he is able to pick out certain key facts and apply them to his everyday life. For example, if a person reads a book about lions, he may be able to naturally put this knowledge to good use if he travels to a country that has lions. By reading many different types of books, people can grow their fact-base, and accumulate and categorize new information.
Children who grow up being able to read have the opportunity to progress faster than they otherwise could. This direct effect provided by the act of reading accelerates a person's development in ways that are probably impossible to measure.