Comprehension means a lot of things to a lot of people. Generally it means to understand, and reading comprehension means to understand written text.
Written text can be fiction but most of it is factual, such as 'India’s capital is New-Delhi' or 'the height of Mount Everest is 29,029 feet above sea level.' Generally, factual information given in a text is easy to understand. The reason why it is easy to understand is simply because it is a fact. Would there be any doubts as to whether New-Delhi is the capital of India or not? In our daily lives we are confronted with facts and, if we want to make our lives as easy as possible, it is important that we can understand the facts that are written.