Question

Why is good character an important part of having good health?

Answer 1

Because if you feel moppy and depressed your body's work flow slows down

Answer 2

In my own words, I think it's because 
If you're a positive person and looking to live happily, you will be having a really good health. Think about it the opposite way, if you were always sad, crying and depressed you won't be healthy, will you?