 In the <unk> on the Mount , Jesus recalls the commandment , " You shall not kill " and then adds to it the <unk> against anger , hatred and vengeance . Going further , Christ asks his disciples to love their enemies . The Catechism asserts that " it is legitimate to insist on respect for one 's own right to life . " Kreeft says , " self @-@ defense is legitimate for the same reason suicide is not : because one 's own life is a gift from God , a treasure we are responsible for preserving and defending . " The Catechism teaches that " someone who defends his life is not guilty of murder even if he is forced to deal his aggressor a lethal blow . " <unk> defense can be not only a right but a grave duty for one who is responsible for the lives of others . The defense of the common good requires that an unjust aggressor be rendered unable to cause harm . For this reason , those who legitimately hold authority also have the right to use arms to repel <unk> against the civil community entrusted to their responsibility . 
