John Calvin Commentary Numbers 31:11

"And they took all the spoil, and all the prey, both of man and of beast." — Numbers 31:11 (ASV)

And they took all the spoil. It was a sign both of their disinterestedness and modesty that they brought the spoils, which they had taken in the ardor of battle, to Moses and Eleazar; nor was it a mere empty and pompous ceremony, as many boastingly parade the wealth they desire to keep to themselves; but their intention was to acquiesce in Moses's determination regarding its distribution.

For, when Moses soon afterwards allots half of it to the people, they are so far from rebelling against his decision that they do not even murmur. It is clear, then, that in this respect they were no less submissive than they had been when, at the outset, they took up arms and boldly went forth to battle, while the rest were quietly reposing out of the reach of the darts.