Matthew Poole and continuators on Judges 7:5

5 So he brought down the people unto the water: and the LORD said unto Gideon, every one that lappeth of the water with his tongue as a dog lappeth, him shalt thou set by himself, likewise every one that boweth down upon his knees to drink .

It is true, there may be natural reasons given, why some did onely Lap of the Water, when others bowed down to drink; from the Temperance, or Fortitude, or Patience, or Strength, or Diligence of the one; and the Intemperance, or Cowardice, or Impatience, or Weakness, or Slothfulness of the other; but these seem to be meer conjectures: The true reason and design of this course, seems to be onely this, That God would reduce them to a very small number, which was likely to be done by this means; for the Season of the year being hot, and the generality of the Soldiers weary, and thirsty, and faint, they would most probably bow down upon their Knees, that they might more fully refresh themselves by a liberal draught, as indeed they did; and it could be expected that there would be but few, who either could or would deny themselves in this matter; especially, when God concurred in the work, and so disposed of the Minds and Bodies of them, that all, except Three Hundred, should lye down to drink.