Lecture 5-3: War, Peace, and Just War Theory

Matthew 5:38-39 sits within the Sermon on the Mount's antitheses, the same pattern Lecture 2-2 examined ("you have heard... but I tell you"): Jesus takes a recognized Old Testament principle — the lex talionis, "an eye for an eye" (Exodus 21:24), itself originally a limit on retaliation rather than a license for escalation — and intensifies it into a personal ethic that goes well beyond limiting retaliation to refusing it altogether, at least at the level of personal response to personal insult ("strikes you on your right cheek" describes an insulting backhand blow, not a lethal attack, which matters for how far either tradition thinks this specific verse extends). Romans 13:4, already introduced in Lecture 5-1's treatment of civil authority, states something that looks, on its face, quite different: the ruler "doesn't bear the sword in vain," language that describes lethal state force not merely as tolerated but as itself an instrument of God's own justice, administered by a "servant of God" against evildoers. The entire dispute this lecture states runs through how these two texts, both undeniably in the canon, both addressed to the same believing community, relate to one another.

The pacifist case, stated at full strength

The pacifist position does not rest merely on Matthew 5:38-39 read in isolation; it rests on a reading of Jesus's whole recorded life and teaching as consistently, deliberately nonviolent even under direct threat and, at the last, under Rome's own instrument of lethal state violence. Jesus rebukes Peter for drawing a sword to defend him in Gethsemane (Matthew 26:52's "all those who take the sword will die by the sword"), refuses to call down legions of angels to prevent his own arrest, and goes to the cross without resistance — a pattern pacifists read as normative for the church, not merely descriptive of what happened to be prudent in Jesus's own specific first-century circumstances.

Stanley Hauerwas, in works including The Peaceable Kingdom (1983), makes an argument more specific and more theologically ambitious than simply "Jesus said not to resist evil, so Christians should not use violence." Hauerwas's central claim is that nonviolence is not one ethical policy the church happens to adopt alongside various others; it is constitutive of what the church is for, because the church exists, on Hauerwas's account, precisely to be a visible, alternative community that embodies in its common life the kind of peace the world's kingdoms cannot produce by their own methods of coercion and violence. On this view, asking "but what if a Christian's nonviolence lets an evil go unopposed" already smuggles in the world's own assumption that effectiveness at preventing harm by any available means is the highest good — an assumption Hauerwas argues the church exists specifically to refuse, trusting instead that faithfulness to Christ's example, not the calculated prevention of every bad outcome, is what the church is actually called to model, even at real and sometimes severe cost. The historic peace churches (Mennonite, Amish, and Church of the Brethren traditions, among others, tracing their position to the sixteenth-century Anabaptist movement) have held a closely related conviction for centuries, often expressed less through academic argument than through consistent communal practice: refusing military service, refusing lethal self-defense, and accepting real historical persecution and martyrdom rather than take up arms, understanding this posture as a direct extension of Christ's own example rather than a separate policy question about state warfare specifically.

The just war tradition, stated at full strength

Augustine, writing in the early fifth century partly in response to Rome's sack by Alaric's forces in 410 (an event some pagan critics blamed on Rome's turn to Christianity, weakening its will to fight), laid the foundation the just war tradition still builds on. Augustine's starting point is not enthusiasm for war but a sober judgment that a fallen world sometimes presents a choice not between violence and peace but between different kinds and directions of violence — an unjust aggressor's violence against the innocent, and a legitimate authority's restraining, defensive use of force against that aggression — and that refusing the second in the name of nonviolence does not actually produce peace; it simply leaves the first kind of violence unopposed and its victims undefended. Augustine reads Romans 13:4 as directly relevant here: if Paul can describe the state's bearing of the sword as itself a form of service to God's own justice, then a Christian serving that legitimate function (a soldier under lawful authority, not a private individual taking vengeance into their own hands) is not thereby acting outside Christian ethics but within a divinely sanctioned exercise of restraining evil that Romans 13 itself describes.

Later thinkers systematized Augustine's insight into named criteria a war, and a specific act of war, must satisfy to be considered just — criteria meant to constrain when and how force may be used, not to license it broadly. Just cause requires a genuine wrong to be righted or prevented (defense against aggression is the clearest case; the tradition treats purely offensive war for gain with deep suspicion). Legitimate authority requires that only a properly constituted governing authority, not private individuals or groups, may declare and wage war — directly connecting to Romans 13:4's language of the ruler specifically, not the individual believer, bearing the sword. Right intention requires that the actual aim be restoring a just peace, not vengeance, conquest, or national glory, even where the stated just cause is genuine. Last resort requires that non-military means of resolving the conflict have been genuinely exhausted, not merely considered and set aside for convenience. Proportionality requires that the anticipated harm of waging the war not exceed the good it aims to secure — a criterion capable, this lecture stresses, of judging even a war begun with genuine just cause to have become unjust in its later conduct if the harm inflicted grows disproportionate to the wrong being righted. Discrimination requires distinguishing combatants from non-combatants and directing lethal force only at the former — the criterion most directly at stake in contemporary debates over aerial bombardment, sieges, and other tactics that predictably harm civilian populations.

It is worth stating plainly, against a common misreading of this tradition, that just war theory is not a blank check for any war a Christian's own nation happens to undertake. A war lacking a genuine just cause, or one that fails proportionality by inflicting harm grossly disproportionate to the wrong it addresses, or one that fails discrimination by treating civilian casualties as an acceptable cost rather than a serious moral constraint, is, on the just war tradition's own terms, an unjust war a faithful Christian committed to this framework should oppose or refuse to participate in — the tradition supplies grounds for principled objection to specific wars, not merely a general justification for warfare as such.

Where the two traditions actually diverge

Both traditions, this lecture insists, take Christ's teaching and the whole canon's witness with genuine seriousness; neither is a caricature of the other, and stating the dispute honestly requires resisting the temptation to reduce either side to "ignoring the hard texts." The real point of divergence concerns how Matthew 5:38-39's personal ethic relates to Romans 13:4's institutional one. The just war tradition reads these as addressed to different actors performing different roles: the Sermon on the Mount governs a believer's personal response to personal insult and injury, while Romans 13 governs the state's distinct, divinely authorized function of restraining evil within society — on this reading, a Christian can, without contradiction, personally forgive an enemy's insult (Matthew 5) while also serving, under lawful authority, in a state's legitimate defense against unjust aggression (Romans 13), because the two texts are simply not addressing the same question. Hauerwas and the peace-church tradition reject this division as a false one: on their reading, Jesus's teaching is not narrowly personal etiquette but a description of the church's whole way of being in the world, and Romans 13's acknowledgment that the state, as a fallen-world institution, does in fact use the sword is a description of how the world's kingdoms function, not a positive commission handed to individual Christians to take up that function personally — Paul describing what states do, on this reading, is not the same as Paul authorizing believers to do it.

This is a genuine exegetical and theological disagreement about how two clearly canonical texts relate to each other, not a case where one side has simply failed to read the other's proof text. Readers of this course, coming from traditions on both sides of this line, should expect to find real force in the argument they do not ultimately hold, and should be able to state the other position in a form its own defenders would recognize as fair — which is the standard this lecture has tried to meet for both.

5. Going to the Sources

Augustine's City of God, Book XIX, contains his most developed treatment of just war reasoning, framed within his larger argument (already engaged in Lecture 4-1) about the earthly city's disordered loves — Augustine's point there is that even a just war is fought within, and marked by, a fallen world's tragic conditions, never celebrated as an unambiguous good; reading this chapter directly corrects a common misreading of just war theory as a triumphalist or war-affirming position, when Augustine's own tone throughout is closer to sober lament over a genuine necessity than to enthusiasm.