Do not Kill
One must not deliberately kill any living creatures, either by committing the act oneself, instructing others to kill, or approving of or participating in act of killing. It is a respect to others' lives.
One should not deprive others (animals not excluded) of the right to live. If one is hurt or killed, one's family, relatives, friends will suffer. It is the cause of rebirth in Three Evil Paths. The effect of killing to the performer are brevity of life, ill health, handicapped and fear.
In observing the first precept, one tries to protect life whenever possible. Furthermore, one cultivates the attitude of loving kindness to all beings by wishing that they may be happy and free from harm.