John Calvin's Bible Commentary
Numbers 31:25
25.And the Lord spake unto Moses. A most equitable distribution of the booty is here described, in which the law of proportion was so well observed that, whilst the soldiers were not defrauded of the reward of their labor, at the same time some advantage accrued to the rest of the people in whose name the war was carried on. The share of the multitude was indeed small, for the same proportion was awarded to the 12,000 as to the remaining 600,000. But, since the booty had been already won by the soldiers in right of their victory, it ought not to have been a cause of complaint to the people who had not borne arms, that they received an honorary gift, although it might be of little value. And assuredly it would have been a shame that those who remained in the camp should be altogether without any part of the spoil, as if they had been convicted of cowardice, whereas it did not depend on themselves that they had not taken part with their brethren in the conquest of the enemy. For it was from no want of courage that they had escaped the burden and the perils of war, but they had modestly allowed the general glory to be appropriated by a few, because it had so pleased God. But, whilst it was just that some of the fruits of the victory should be communicated to all, so it. was no less right that the fuller and more liberal reward should be received by those who had borne the whole brunt of the war.
It appears to some that David pursued the same rule, when he distributed the spoil equally amongst his followers who had gone down to the battle, and those who had stood by the baggage. (1 Samuel 30:24.) In my opinion, however, what David then decided was very different; for if the portion of those who remained with the baggage had been equal with that of those who were actually engaged, it would have been far more advantageous to remain out of the reach of the weapons. For, when a battle is fought, only a few men out of a large army are generally left with the baggage, and thus half the booty would have accrued to a few idlers. The partition, therefore, which is there mentioned, must have been an equal distribution to each individual; and very justly did David enjoin that those who remained stationed in the camp should have a full share of the spoil, lest (210) the condition of those should be dissimilar who were under the operation of the same rule. But in this case the actual warriors are justly rewarded above those who quietly attended to their own domestic cares.