Why do humans need the sun?

The sun helps the body to produce Vitamin D, which enables to body to absorb calcium to build strong bones and teeth.

to help grow their plants

Answer

Some people say that sun does not give any good to us. Well, do not be fooled. If were going to remember our Biology class, sun is the prime source of the energy that we get from the food we eat. It provides energy and photosynthesis that is needed for the plants to grow; same with all the living things in this world. If the sun never existed, nothing is this world could have existed either. Our God created lives on earth for us to appreciate, and therefore we have to cherish the gift of light and heat that is being given to us in order to continue of daily lives and activities.