“What about the prohibition, ‘You shall not kill,’ which is also there? If killing is evil in every respect, how will the just who, in obedience to a law, have killed many, be excused from this charge?” The answer to this question is that he does not kill who is the executor of a just command.
It is significant that in Holy Scripture no passage can be found enjoining or permitting suicide either in order to hasten our entry into immortality or to void or avoid temporal evils. God’s command, “You shall not kill,” is to be taken as forbidding selfdestruction, especially as it does not add “your neighbor,” as it does when it forbids false witness, “You shall not bear false witness against your neighbor.”
Kill. These precepts are to be taken in their full extent, as prohibiting not only the ultimate act, but every thing which leads to it. Magistrates are authorized to inflict capital punishments. We are allowed also to defend ourselves against an unjust aggressor. But we must never intend to kill him. (Calmet)
The laws will not condemn us, perhaps, if we do; but God sees the heart, and judges. A night thief may be slain, because we know not how far our own lives may be endangered, chap. xxii. 2. (Haydock)
How was it then when he said, “You shall not kill,” that he did not add, “because murder is a wicked thing?” The reason was that conscience had already taught this beforehand. He speaks thus, as if to those who know and understand the point.
