We classify things to make it easy to understand and organize. In the case of organisms, we classify these to study about similar characters, evolutionary relationships, to study genetic patterns.

Classification is the need to get proper clarity about anything or any topic and Organism is any individual entity or life form that embodies the property of life. So, the classification of an organism is a necessity for better information and categorization. Let’s take the example of a school or any department, every where we will find classification like a school is further classified into the wing, then classes, then sections, then roll no and names. Similarly there are a number of species having the number of qualities, similarities, differences, and furthermore detailing which one can only find if we have classified data of that organism in the form of records or formats. This need for identification brought about the invention of the classification of organism.        
For more explantion on this answer view this lesson
Classification of organism