If you do the math, God chose only 1% of the people for this task.
Judges 7:3 Now therefore go to, proclaim in the ears of the people, saying, Whosoever is fearful and afraid, let him return and depart early from mount Gilead. And there returned of the people twenty and two thousand; and there remained ten thousand.
Judges 7:6 And the number of them that lapped, putting their hand to their mouth, were three hundred men: but all the rest of the people bowed down upon their knees to drink water.
Gill describes the way of lapping, but from the context we see it was just God’s way of selecting this very small fraction of the people.
Judges 7:2 And the LORD said unto Gideon, The people that are with thee are too many for me to give the Midianites into their hands, lest Israel vaunt themselves against me, saying, Mine own hand hath saved me.
and the Lord said unto Gideon, everyone that lappeth of the water with his tongue, as a dog lappeth, him shall thou set by himself; this has led some, as particularly Grotius, to think of the Egyptian dogs; of whom Aelianus relates (b), that they do not drink at once freely, and to satiety, being afraid of the crocodiles in the river; but run about the bank, and by stealth snatch a little here and a little there, and so satisfy themselves: but the allusion here is to dogs in common, whose usual way it is not to sup in, and drink a drought, but by putting out their tongues to lick and lap water with them, as Aristotle (c) says all creatures do that have teeth like saws; and the likeness between the drinking of these men, to be observed lay not in anything else but in the single action of lapping; for they first took the water in the hollow of their hands, out of the stream, and then lapped it, as in Jdg 7:6 whereas a dog does not and cannot take water that way; and this lapping was standing upright, whereas dogs in common, as Aelianus in the same place suggests, bow themselves, and lap as much water as will satisfy their thirst; and by this these men were distinguished from those that bowed on their knees to drink; for had they not taken up water in their hands, they must have bowed down on their knees to have lapped, as well as those did, to sup it, or take in a large draught of it; now all those that thus lapped were to be set apart by themselves; but whether they were to go with Gideon or not, as yet he knew not: likewise everyone that boweth down on his knee to drink; were to be set by themselves also, but which of those were to go with him is after related.