Reply to Objection 1. As Augustine says (Contra Faust. xxii, 70): "To take the sword is to arm oneself in order to take the life of anyone, without the command or permission of superior or lawful authority."
On the other hand, to have recourse to the sword (as a private person) by the authority of the sovereign or judge, or (as a public person) through zeal for justice, and by the authority, so to speak, of God, is not to "take the sword," but to use it as commissioned by another, wherefore it does not deserve punishment.
And yet even those who make sinful use of the sword are not always slain with the sword, yet they always perish with their own sword, because, unless they repent, they are punished eternally for their sinful use of the sword.
Reply to Objection 2. Such like precepts, as Augustine observes (De Serm. Dom. in Monte i, 19), should always be borne in readiness of mind, so that we be ready to obey them, and, if necessary, to refrain from resistance or self-defense.
Nevertheless it is necessary sometimes for a man to act otherwise for the common good, or for the good of those with whom he is fighting.
Hence Augustine says (Ep. ad Marcellin. cxxxviii): "Those whom we have to punish with a kindly severity, it is necessary to handle in many ways against their will. For when we are stripping a man of the lawlessness of sin, it is good for him to be vanquished, since nothing is more hopeless than the happiness of sinners, whence arises a guilty impunity, and an evil will, like an internal enemy."
Reply to Objection 3. Those who wage war justly aim at peace, and so they are not opposed to peace, except to the evil peace, which Our Lord "came not to send upon earth" (Matthew 10:34).
Hence Augustine says (Ep. ad Bonif. clxxxix): "We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace."
Reply to Objection 4. Manly exercises in warlike feats of arms are not all forbidden, but those which are inordinate and perilous, and end in slaying or plundering. On olden times warlike exercises presented no such danger, and hence they were called "exercises of arms" or "bloodless wars," as Jerome states in an epistle [Reference incorrect: cf. Veget., De Re Milit. i].