Morality is those actions and behaviors that lead to the good health and well-being of individuals and communities.  So what does "well-being" mean?

Well-being is a state of being happy and prosperous.  And why would being happy and prosperous be important?  Presumably, everyone wants to live, as that seems to be what drives us.  When we lose focus on the necessities of life and we start feeling ill and miserable, our happiness and prosperity fade.  We lose our well-being.  

The actions and behaviors we participate in, which cause our well-being to fade, are by definition, immoral.  This could be benign things like not getting enough sleep, not eating right, and not exercising enough.  It could be more offensive actions and behaviors such as consuming poisonous substances or doing things to our body, which the body cannot safely do. Imposing such actions and behaviors on others reduces their well-being, and is also immoral.

Well-being is not a passive state.  It is an active state, which requires vigilance and attention to maintain.  It could be said that well-being induces us to continue with our living body as long as our happiness and prosperity continues.  Well-being is both the cause and effect of itself.  The same can be said for communities of organisms, which as a whole are also living beings.

Well-being is an essential characteristic of life, which is one of the reasons why morality is so vital to individuals and communities.