"May the praise of God be in their mouths and a double-edged sword in their hands, to inflict vengeance on the nations and punishment on the peoples, to bind their kings with fetters, their nobles with iron, to carry out the sentence written against them. This is the glory of all the saints." (v.6-9)
Whatever dynamic relation the New Covenant inaugurates with the Old, whatever Jesus meant when He said "You have heard...but I say to you," whatever occurred with God's own command on the cross (Eph.2:15), one thing that can never be said about the Law is that it was evil, or required evil behavior of its subjects.
Pacifists who imply or straight out say that "war is always evil," are blasphemers. Pacifists who shilly-shally and admit the occasional justice of war but expect some subjective attitude of shame, sadness, mourning and the like to accompany its participants are poor exegetes.
What we learn from the above Word of Jesus (yes modern scholars, the Second member of the Trinity was not strangely absent in the deliverance of the Law and Prophets, go snivel in a corner you feckless heretics) is that the carrying out of God's sentence against the nations via warfare is the GLORY of his saints. It is their honor, their dignity, their joy.