Killing, deceiving, or misleading someone's mind (soul) by driving him to insanity or mindless wasteland (by preaching a fake religious doctrine or faith) is the worst of all the karma you can inflict on yourself. - Edward Rim

Driving someone to insanity is a much more serious crime than murdering someone, so the worst of all karma.

Why do I say this? Because insanity murders the mind (soul) along with killing the body by making it useless or purposeless.

Karma is justice. It does not reward or punish. It shows no favoritism because we all have to earn all that we receive. Karma doesn’t predestine anything. We create our own causes and Karma adjusts the effects with perfect balance. - Mary T. Browne

This quote in my opinion most succinctly defines karma. Karma is all self-creation. There are no other people but you who are both the sinner and executioner.

Searching all directions with your awareness, you find no one dearer than yourself. In the same way, others are dear to themselves. So you shouldn’t hurt others if you love yourself. - the Buddha

These words by the Buddha are so resonating with me these days. 

I consider my life the most precious thing to myself; I am doing all I can to protect my life and my wife's— for her life is the most precious thing to her—while there are people who are toying with our lives as if the value of our lives to us is far less valuable than their lives to them.

Like the Buddha said, "You find no one dearer than yourself. In the same way, others are dear to themselves."