Citta and Cetasika

What the use is of knowing the details about citta and cetasikas?

Extract from Cetasikas: Introduction

The reader may wonder what the use is of knowing the details about citta and cetasikas. Citta and cetasikas are not abstract categories, they are active at this very moment. We could not see, hear, think, act, be angry or have attachment without cetasikas. Seeing, for example, is a citta. It is the citta which cognizes colour or visible object. In order to perform its function it needs the assistance of cetasikas, such as contact, which contacts visible object, or one-pointedness, which focuses on the object. It is important to have more understanding of cetasikas. We should know that defilements are cetasikas and that good qualities are cetasikas. They arise in daily life and when they appear we should investigate their characteristics. Otherwise we would not know what is right and what is wrong. We would not know when defilements arise and how deeply rooted they are. If the Buddha had not taught in detail about defilements we would only have a vague idea about them. How could we see the danger of defilements when they are unknown to us? How could we develop what is wholesome if we would not know the characteristics of wholesome cetasikas and the different ways of good deeds?