You child will be able to hear how reading sounds like when it's done by an adult, how it is different from his own reading. He carries the echo of the sound in his ear as he learns to read alone.
Even when a child develops enough confidence in himself by reading to his parents and younger siblings, he still needs to hear stories read aloud for him too. The growing independence in reading alone is strengthened by the praise he receives from his listeners.
Reading aloud is a social event, your child learns not only stories, he learns about life, his family, his place in the world. While reading a story, we tend to talk about it and even after the reading is over, we still continue to talk about it. Events from stories can be related to everyday life, reinforcing the story in your child's mind.
Hearing a story in a group at the library or school cannot compare to hearing a story read aloud to you by your own parent at home. When you read to your children, you are not only teaching them about the material they are reading. You are telling them that they are important to you, that they are safe and secure with you by their side.
All children needs to receive messages like these, to show that you feel that they are important to you.