Even if you don't fully understand it the first time around, these are cultural reference points, so at least when you hear someone reference them, you'll have an idea what they are talking about and can get the point of what the adults are talking about. Then later if you ever read it again, you also have a better understanding of its place and get a better second pass understanding.

There is also the role of simply communicating to the next generation that society values these books, and they are important for some reason. Even if you only get one shallow layer of meaning at the time. Same with history and everything else. It's a time to get a first taste of what these things feel like.