Explain: "some books are to be tasted others to be swallowed and some few to be chewed and digested."

In this extract from Bacon's 'Of Studies', Bacon says that all books in the world do not deserve equal number of attention of its readers. He classifies books into three groups, the first which are to be read in parts only and not in detail. Second, there are some books which should be read from cover to cover and do not deserve mindful studies. It is the third type, of which there is a small number which deserve to be read thoroughly and diligently as they provide matter which can enrich the readers with their wisdom and knowledge.