I came across a very good reflection on Luther's Two Kingdom Theology by a Pastor of the Reformed tradition who gives special attention to Luther's view on the Crusade against the Turks. Very interesting Read that is very much in line with the Wikipedia article IMHO.
"By Steven Wedgeworth
Martin Luther’s political theology has fallen on hard times. While it was once common to give him credit for the emergence of modern political liberties, Luther’s legacy has, especially since the second world war, soured. Many have claimed that he set the stage for an unholy sort of sacred nationalism, while more recent commentators say that Luther had no political theology at all, but was instead content to take a “hands off” approach, ceding everything to an emerging secular state.
Most of this diversity of interpretation stems from a failure to read Luther’s politics in light of his foundational theological commitments, especially his doctrine of justification by faith alone. Luther’s political thought is actually entirely consistent with his more basic theological affirmations. And there’s one place where Luther’s political thought is unambiguous and deserves praise, even from the most ardent critics. Martin Luther thoroughly criticized the medieval notion of crusading and, in fact, rejected the entire concept of sacralized violence. While a great defender of the just war, Luther entirely condemned the notion of holy war. Soldiers could indeed be saved, but they could never win the Cross by the sword.
Luther’s Two Kingdoms
To understand Luther on politics, we must know what he means by his doctrine of the “two kingdoms.” Too easily confused as a theory of “church and state,” Luther’s two kingdoms were actually entire dimensions. The earthly kingdom had to do with all rule or governance on the earth, or any government that could legitimately make use of coercive authority. This earthly kingdom included the civil magistrate, but also Christian families and even the political or governmental aspect of the visible church. In short, anything that had earthly laws which could expect compliance and enforcement could be described as an aspect of the earthly kingdom. The spiritual kingdom, on the other hand, was God’s jurisdiction over the human soul, concerned with heavenly or spiritual goals. Because of his understanding of St. Paul, Luther taught that this kingdom was free from all law. It was, instead, the immediate reign of Christ through His Spirit in the heart of all believers. This spiritual kingdom could never be equated with an earthly magistrate, nor even the institutional church as such. It was truly “not of this world.”
Luther explains this distinction on several different occasions. In his pamphlet On Secular Authority, he says this:
The first point to be noted is that the two parts into which the children of Adam are divided, the one the kingdom of God under Christ, the other the kingdom of the world under [secular] authority, have each their own kind of law. Everyday experience sufficiently shows us that every kingdom must have its own laws and that no kingdom or government can survive without law. Secular government has laws that extend no further than the body, goods and outward, earthly matters. But where the soul is concerned, God neither can nor will allow anyone but himself to rule.
Luther grounds these two governments on the distinction between the righteousness which comes from the law, which is to say earthly righteousness judged by good works, and the righteousness which justifies a man before God, the righteousness which comes by faith alone. He makes this connection between justification by [Christ] alone and the two kingdoms directly in his treatise On Soldiers:
I would have it understood that I am not speaking, this time, about the righteousness that makes men good in the sight of God. For the only thing that can do that is faith in Jesus Christ, granted and given us by the grace of God alone, without any works or merits of our own, as I have written and taught so often and so much in other places; but I am speaking here about external righteousness which is to be sought in offices and works. In other words, to put it plainly, I am dealing here with such questions as these, — whether the Christian faith, by which we are accounted righteous before God can tolerate, alongside it, that I be a soldier, go to war and slay and stab, rob and burn, as one does to enemies, by military law, in times of war.
This relationship is essential to understanding Luther’s view of politics. While earthly government and the laws actions that accompany them can be good, they can never be “heavenly” or of the sort of righteousness that justifies a man before God and secures his eternal salvation.
Luther does not use this distinction to allow for sinning in politics. He says that earthly laws should be founded on justice, defined by the natural law and God’s moral teaching in Scripture. He even says that they should measure themselves according to love. But earthly politics are always provisional, and they are always limited in goal. They are concerned with the business of this world and must stop short of reaching into men’s souls. Earthly laws have no jurisdiction in the spiritual kingdom.
Since Luther distinguishes the two kingdoms in this way, he can apply the teachings of Christ in the Sermon on the Mount to all Christians, but in a distinctive manner. His central argument against Roman Catholicism in On Temporal Authority, is that they restrict the teachings of Christ regarding “resist not evil” (Matt. 5:39) to those Christians who pursue the “counsels of perfection.” Practically speaking, this means that only monks, nuns, and certain clergymen carry the burden of Jesus’ ethical teaching, while the “ordinary Christian” must be content to disobey or disregard it as impossible. But for Luther, all Christians should obey this teaching of Christ, and that must mean that it is possible. However, since Luther also believes that the Bible is clear that the sword is a divine ordinance endorsed by the New Testament (particularly Romans 13:1-7), he argues that there must be a consistent way for a Christian to both “resist not evil” (Matt. 5:39) and “avenge wrath on him who practices evil” (Rom. 13:4). The solution is found in the doctrine of the two kingdoms.
Luther explains this duality by appealing to the Christian’s ability to personally bear evil done against him but also employ civil government to protect his neighbor and provide public order and stability:
A Christian should be so disposed that he will suffer every evil and injustice, not avenge himself nor bring suit in court, and in nothing make use of secular power and law for himself. For others, however, he may and should seek vengeance, justice, protection and help, and do what he can toward this. Likewise, the State should, either of itself or through the instigation of others, help and protect him without complaint, application or instigation on his part. When the State does not do this, he ought to permit himself to be robbed and despoiled, and not resist the evil, as Christ’s words say.
In this way, I take it, the word of Christ is reconciled with the passages which establish the sword, so that this is the meaning: No Christian shall wield or invoke the sword for himself and for his cause; but for another he can and ought to wield and invoke it, so that wickedness may be hindered and godliness defended.
Luther uses this very same duality to defend the role of Christians in the army. Christians cannot bear the sword in order to protect their souls, but they can bear it in order to protect their country:
For Christians, indeed, do not fight and have no worldly rulers among them. Their government is a spiritual government, and, according to the Spirit, they are subjects of no one but Christ. Nevertheless, so far as body and property are concerned, they are subject to worldly rulers and owe them obedience. …Therefore, when they fight, they do it not for themselves or on their own account, but as a service and act of obedience to the rulers under whom they are, as St. Paul writes to Titus, “They shall obey the rulers.”
Again, we see a consistent message. Christians do not fight for themselves, nor for Christianity as such. Instead, they fight out of love for their neighbor as they defend earthly goods in a just manner, obeying the rulers God has placed over them.
On War Against the Turk
The effect of Luther’s two kingdoms doctrine is seen most dramatically in his rejection of crusades. Beginning as early as 8th century Byzantium, medieval Christians had held to a form of crusading theology: that they could defend the Christian Church as such through military arms. This ideology came to full flower with Pope Urban II’s infamous Council of Clermont, where he is said to have offered the remission of sins in exchange for liberating Jerusalem from the Turks. Crusading was a sort of “war as penance,” with the result being a sacral violence thought to be carried out in direct obedience to Christ Himself.
Luther rejected such an ideology entirely. For him it was both impossible and repugnant. The Christian does not fight for Jesus with earthly weapons, and no minister should command Christians to use violence for spiritual goals. Building upon what he had already written in On Temporal Authority and On Soldiers, Luther explained his criticism of crusading in another pamphlet, On War Against the Turk. As you might expect, Luther does allow for Christians to join the army and fight against the invading Turkish power. But he is emphatic that they can only do so as earthly citizens, obeying their earthly rulers. They can fight as Germans. They cannot “fight as Christians,” at least not if that means killing Turks in order to spread the kingdom of Christ.
To support this argument, Luther again invokes the two kingdoms:
I say this not because I would teach that worldly rulers ought not be Christians, or that a Christian cannot bear the sword and serve God in temporal government. Would God they were all Christians, or that no one could be a prince unless he were a Christian! Things would be better than they now are and the Turk would not be so powerful. But what I would do is keep the callings and offices distinct and apart, so that everyone can see to what he is called, and fulfill the duties of his office faithfully and with the heart, in the service of God.
The Christian soldier must understand his office: it is to serve the temporal authority and protect the land. The soldier’s office is not to spread Christ’s kingdom or convert the hearts of the enemy by the sword.
Indeed, Luther believes that crusading is a great sin, and he warns against it in emphatic terms:
Again, if I were a soldier and saw in the field a priests’ banner, or banner of the cross, even though it were a crucifix I should run as though the devil were chasing me; and even if they won a victory, by God’s decree, I should not take any part in the booty or the rejoicing.
A few sentences later he adds:
If the banner of Emperor Charles or of a prince is in the field, then let everyone run boldly and gladly to the banner to which his allegiance is sworn; but if the banner of a bishop, cardinal, or pope is there, then run the other way, and say “I do not know this coin; if it were a prayer book, or the Holy Scriptures preached in the Church, I would rally to it.”
Is the Christian’s only recourse against the realistic fear of the invasion of Christendom by Muslim armies, which in fact happened, then, secular warfare? Not exactly. Luther goes on to say that there is a way that the Christian can fight the Turk. They can fight through repentance and prayer.
Christians should renew their spiritual lives with God, and they should call for revival in their own churches. This, Luther believes, will strike a mighty blow against the Turk. Indeed, the power of the gospel is such that over time, even the Turk can be brought to salvation. This will not happen if Christians attempt to spread the gospel by the sword. But it can happen through prayer and holiness. Christian ministers should therefore not preach crusading but rather the cross of Christ. They should hold the gospel before their people’s eyes and let their sword be the Word of God.
Thus was Martin Luther’s political theology applied to the topic of holy war: he could only reject it. Because of the nature of the gospel, Christians can spread Christ’s kingdom exclusively through the Word: through preaching, persuasion, and peaceful means. Only the Spirit will slay Christ’s enemies, cutting them to the heart with the Word and burying them in Christ–in other words, conversion, salvation, and eternal life. And thus, while there remains a place for civil defense and the protection of one’s neighbors and common land, the Christian cannot and must not join the call for crusades. To do so would, in fact, be a great dishonor to the cause of Christ.
Luther is a complex thinker, and he is certainly not without his objectionable moments. But here, with his two kingdoms doctrine, we see a great aid to the kingdom of Christ. The wrath of man can never bring about the righteousness of God, and so the Gospel of Peace ought to be embodied in our refusal to spread it by the sword.”