The divine banner and the human banner do not go together, nor the standard of Christ and the standard of the Devil.  Only without the sword can the Christian wage war: the Lord has abolished the sword.
 Tertullian 

Now we who once murdered one another not only refrain from all hatred of our enemies, we meet death cheerfully for confessing to Christ.
 Justin (same as before) 

We ourselves were well conversant with war, murder and everything evil, but all of us throughout the whole wide earth have traded in our weapons of war.  We have exchanged our swords for plowshares, our spears for farm tools…now we cultivate the fear of GOD, justice, kindness, faith, and the expectation of the future given [...]

Christians, instead of arming themselves with swords, extend their hands in prayer.
 St. Athanasius 

Murder, considered a crime when people commit it singly, is transformed into a virtue when they do it en masse.
St. Cyprian