There have been many attempts to rationalize such matters -by both apologists and heretics- I think there is always something missing in them -especially the route of Marcion and the Manicheans who summarily rejected God as described in the OT -a strategy unanimously rejected by the Orthodox fathers of the first Christian millennium, but also of many Christian thinkers who have sought to minimize the problems involved. I'll also discuss Num 31 specifically. Obviously many sections of the OT relate to Israel as a nation at war. My personal view is that war can never strictly speaking be considered rational, holy, or just even when it has the ostensible sanction of God (explanation below). Having qualified the situation as being beyond fully resolving, I'll share some examples -not fully satisfactory perhaps- which have been offered toward that end.
If one wanted to presume there could be some sort of a "rationalist resolution," it might come along the lines Just War Theory in Western philosophy and theology which has remained a major field of inquiry from Augustine to the present. Without entering fully into this maze, we can mention some commonly held principles within this tradition:
War must be declared and engaged in by proper authority (Rom 13:4).
All attempts at peaceful negotiations have first failed (Rom 12:18; Heb 12:14; Deut 20:10; i.e. war must be undertaken only as a last resort).
Justly waged (Deut 20:19, 20 contra “scorched earth”; avoid unnecessary destruction, especially of that essential to continuation of life after war; avoidance of indiscriminate killing of non-combatants, etc.).
Protection of the innocent is a demand of love (Gen 14:14f).
Persons are more valuable than things (the OT represents the first time in human history this principle was affirmed).
Persons who respect personhood are to be preferred over those who do not.
Many lives are of more value than few lives.
Realistic expectation of success.
Even Wolfhardt Pannenberg, who ardently maintains no war is or can be ‘just,’ agrees a nation may have sufficient grounds to engage in war, e.g. in the instance of unprovoked attack, or even pre-emptively to “anticipate an attack that is certain to come.” (Pannenberg, Ethics, p. 179).
Such principles and their apparent (at least relative) biblical warrant notwithstanding, I fully embrace the kinds of reservations expressed by Pannenburg; Bloesch also cautions us about speaking of war as ‘just’ in the sense of something which might be viewed as untainted, even when it is divinely sanctioned:“… sin is always present in war. Indeed, sin is accentuated in war. It comes to fruition in war, even if war has God’s secret sanction. Because its immediate cause is sin, it brings with it the penalty of divine judgment. Because of blood on his hands, David was not permitted to build the temple, even though the wars he engaged in presumably had God’s blessing
(1 Kings 5:3; 1 Chron 22:8 )” (Donald Bloesch, Freedom for Obedience
, p. 290).
Though the OT speaks of Yahweh as a Warrior, OT scholar Peter Craigie reminds us that "War is a human activity, furthermore, it is a sinful human activity, revealing man's inhumanity to his fellow man. To describe God as a warrior [cf. the Song of Moses] is thus to say that God participates in human history, through sinful human beings, and through what have become the "normal" forms of human activity. Insofar as God is active in the world through human lives, he is employing fr his purpose sinful persons. To state it another way, God employs for his purpose of bringing salvation to the world the very human beings who need salvation [footnote: It is significant to note that 'salvation' in the Old Testament is a translation of a Hebrew word which has the primary sense of 'victory']. One point is becoming very clear: the activity of God in this world insofar as it involves human beings as agents, must always appear , to a greater or lesser extent, to be associated with sinfulness. But there is another side to this difficult statement. The participation of God in human history and through human lives does not primarily afford us a glimpse of his moral being; it demonstrates rather his will and activity"
(Peter C. Craigie, The Problem of War in the Old Testament
A very good statement of the dialectical tension involved in all violence comes from Alveus
My current opinion is that all violence is tied inextricable with sin and that even to kill... another in defending a weaker one is tainted with corruption and sin. It is not "justified" or made righteous because there was some cause for it. When we have to act in such ways, it's still a sin that requires contrition and inner turmoil, not simply something with a seal of absolute approval. But I just can't get on board with the systematic idealistic type of pacifism that [some are] promoting because I think that it is the lesser of two evils, so to speak, to stop the hand of a vicious man against a helpless one then to let his violence be carried out against them. Because I would consider it a great evil for anyone to let children be slayed without cause. Dying for one's faith is one thing, but sacrificing others to one's own ideals is quite another.
Some of the relevant narratives do not reflect Israel as the lawgiver or priest to the nations so much as Israel the nation struggling to survive. Some writers such as Bloesch suggest the possibility that nations and governments bearing the sword may sometimes reflect the shadows as much as the light of God in a fallen world...
"To kill in the name of Christ and in order to advance the kingdom of Christ is expressly forbidden by Jesus (Mt 26:52, 53). Yet sometimes we have to take up the sword in order to preserve life, and this is permitted in the Bible but as something that pertains to the passing aeon, the world of sin and darkness, not to the new age of the kingdom of God. Since we belong to the old age as well as to the new, we act in two roles: as responsible citizens of the state, which can only maintain itself by force, and as ambassadors of the kingdom of Christ, which maintains itself solely by works of faith and love. The ethic of Jesus expressed in the so-called Sermon on the Mount was given to disciples, not to nations. If the radical ethic of nonresistance were applied directly to nations, it would mean the end of all civil government… The principle of nonresistance or no retaliation can be a goal or ideal in the social arena, but never a political strategy of a nation” (Donald Bloesch, Freedom for Obedience
, pp. 293).
Life for us is of incalculable value, and cannot be placed in a utilitarian calculus. God alone can ever do this since He sees life not merely as mortal (*penultimate*) but in association with eternity, which we cannot see clearly enough to adjudicate *ultimately*whatever God might do providentially through sinful humanity. Certainly we must not countenance constructing some sort of utilitarian ethic of war from the OT narratives.
“All these stories remind us that God’s commandment against killing protects life, but it does not enthrone life. It was given to preserve life, but not to idolize life. Life is something good, but it is not unconditionally sacred in the biblical perspective. Human life proceeds from God and is designed to give glory to God. Since it is a gift from God, life must be respected and may be taken only for the sake of life... (ibid, p. 207)
The worst brutalities and horrors in human history result from situations where the very survival of a people was at stake. The revulsions of war, and the horrors of survival when it hangs by the slimmest of threads are among the worst of the grim realities of life. Destruction of innocent women and children was a common feature of 20th century warfare, as most if not all centuries known to historians. It is not just “the other guys” who perpetrate such horrors. Not just Stalinist Russia, Maoist China, the Khmer Rouge, Islamist combatants or Nazi Germany, but also Britain under Winston Churchill, who after long siege by German bombing raids on English soil, made the decision to heavily bomb civilian cities in Germany where there were no military or industrial targets in the hope that the resulting horrors would create political pressure for Hitler to halt his own bombing campaigns, i.e. the decision to kill innocent men, women, infants and children without discrimination. Since the strategy did not work, these deaths were probably for nothing. Churchill also contemplated a large-scale assault on German civilians using poison gas. Napalm was used extensively where destruction of non-combatant peasant villages resulted in Vietnam. The bombs dropped at Hiroshima and Nagasaki were aimed at civilians as well. In this case many more lives were saved than lost, but it would take the utmost in callousness to claim that we are thereby absolved from the utter horrors that were committed there.
Num 31:54 describes Moses’ last military campaign (against the Midianites) continuing the account of chapter 25 of Israelite apostasy at Baal Peor, which very nearly led to the complete destruction of the Hebrew nation
. It is easy for the modern reader to miss the very real mortal danger this situation presented to the survival of the other followers of Moses in the great desert wastes, men women and children, who were not a part of this apostasy. With a significant loss of their men, Moses’ people would likely never secure a homeland. The Midianites, unable to defeat Israel militarily, had conceived a plot to seduce many of her men through sexual temptation to abandon their God, thereby vitiating the source of their unity, strength, and mission. Without the hearts of her men, the rest of Israel would have soon become helpless in the desert, unable to survive, and unable to continue their mission. The Israelite men known to have partaken in this seductive idolatry were given the death penalty (Num 25:5). Idolatry aside, in a very real sense their actions consigned the lives of those who did not follow their path to certain failure, and serious mortal danger. Midian was placed under the ban as a result of that event (Num 25:17). So seductive were the enticements of the Peor that Israel is recorded still under their spell in Joshua’s day (Josh 22:17).
What I will not end my post with in this case is something to the effect of "I hope that helps..." -this is, I think, a dark and unfathomable mystery. But I will not speak against the God of the OT in the manner of the Marcionites and the Manicheans of old as I do not have a full enough picture to stand in judgment of God; it is rather He that must judge me.