That was one of Korach’s seemingly valid questions to Moses and Aaron. Another was, “If I have a house full of religious books, why do I need a m’zuzah on the doorpost?”
Let’s apply the second question to the increasing number of Jewish homes that have whole sets of religious books on their shelves. No house of this kind is without m’zuzot.
Of course if Korach had his way they would say, “A m’zuzah contains a scroll with a few Biblical verses. My whole house is full of books with Biblical texts and commentaries. Surely I am exempt from the law of m’zuzah?”
No one, however, actually argues like this. The fact is that you can have all the religious books in the world, but what matters is not which books you have but your attitude to them.
If they are merely library items, literary tomes, interesting products of the human mind, a m’zuzah is needed, but it may not be able to confer sanctity on books, shelves, home, or people. But if the m’zuzah says, “I am a sign that these works are the word of God, that these books are sacred and there is a spirit of holiness in the house”, it has a value far beyond rubies.