Religion or rules of behavior were designed to limit the killing so as not to destroy our selves with too much killing.
There are many ways to destroy ourselves in an era of unrestrained hedonism.
Modern society is a mechanism for inculcating bad habits, especially the habit of seeking instant pleasure, intoxications and distractions; a habit of regarding ourselves as passive recipients for entertainment. A devout life is not so much about a flash of understanding but is mostly a matter of using insights into truth in building-up good habits; and this can be influenced by our will. A devout life enables one to build these habits and most importantly successfully pass them on to our children.
Whatever sense we make of this world, whatever value we place upon our lives and relationships, whatever meaning we ultimately give to our joys and agonies, must necessarily be a gesture of faith. Whether we consider the whole a product of impersonal cosmic forces, a malevolent deity, or a benevolent god, depends not on the evidence, but on what we choose, deliberately and consciously to conclude from that evidence
If we decide to leave the questions unanswered, that is a choice; if we waver in our answer that too is a choice: but whatever choice we make, we make it at our peril.
What we choose to embrace, to be responsive to, is the purest reflection of who we are and what we love. That is why faith, the choice to believe, is, in the final analysis, an action that is positively laden with moral significance.