Compassion for yourself and others is the key to longevity (a long life)

And hatred, anger and vindictiveness is the key to a very short one (for most people).

Most people who hate others are vicariously hating themselves. Most people who kill others are also vicariously killing themselves.

So, whether you are killing yourself by killing or harming others or not, you are still killing yourselves slowly or quickly.

Conversely, Compassion for others is compassion for yourself. Compassion for yourself acts out as compassion for others. How you feel about yourself you tend to give to others as well.

As you are compassionate to others you tend to feel better about yourselves and your own lives. As you are compassionate to yourself you tend to give others the compassion your give towards yourselves.

So, making a vow of harmlessness towards yourself and all others benefits yourself first.

How?

It leads to a longer life.

How?

The cells in your body feel the compassion and caring you are feeling and think: "I must be a good person because the soul living in my cells and brain cells believes this is true."

So, those cells whether muscle or brain or other cells function better. As you are compassionate towards yourself you tend to eat better, drink less, and take drugs less. Your brain clears up you start to feel better about yourself because your mental and physical health is better and better.

Conversely, as you hate yourself or kill others rather than killing yourself, you tend to drink more alcohol, take more drugs and so are in a homicidal and suicidal spiral usually ending in death from drugs, alcohol, bad decisions in general or just crashing your car or jumping off a cliff or some other suicidal homicidal behavior.

So, longevity (if this is what you want) is based entirely upon treating yourself and all others right.

and the opposite creates the opposite.

This is only logical if you think about it while you are sober and not taking drugs or eating bad foods.