Why do we need to study culture?

Primarily because it is misunderstood. It refers to ways of life, to what's important to each different culture, and we study it, so that we might value these differences. Culture is expressed in actions and Language, its expressed in the Arts, and if we look back in time, where did our culture come from, in ancient history, we learn a lot from many sources - We have different religions, and some of us and our cultures are more overt spiritually, and through spirituality, a value system is transmitted, right now although it is not my main culture, that is what I was born into, I can see a Bhuddist setting and hear a gong resounding and have an idea of Zen and its calmness and teachings. Through the world now and globalisation, we share cultures, and we can be influenced by other cultures, although we are aware of the culture into which we were born and differences which are important to peoples of the world.
So if I travel to China, for example on business, I will from politness learn about what is important to the Chinese culture and what an exciting subject to study. Good Luck.