Question

In lesson “Kindness and Law” 1, you explain that law is acting according to rules, and kindness is acting not according to the rules.
According to the law, I am not obligated to give charity, and therefore if I give, then I am performing an act of kindness (if we ignore the commandment of charity).
 
My question is this: it is true that kindness is an action that is not according to civil law, but it is an action that is according to moral law. That is, I am morally obligated to act with kindness. And if so, then again kindness is not a voluntary action, but rather I am obligated to act according to kindness.
So how does this fit together—that on the one hand the connotation of kindness is a voluntary act of beneficence and so on, while on the other hand it is not voluntary but rather a moral obligation?