Mesillas Yesharim (ch. 11) cites the interpretation of Medrash Rabba on a verse in Shir Hashirim:
"שניך כעדר הרחלים," מה רחל זו צנועה, כך היו ישראל צנועים וכשרים במלחמת מדין.
"Your teeth are like a flock of ewes" (Shir HaShirim 6:6). Why are the warriors of Israel compared to a flock of ewes? For the following reason: Just as a ewe is modest, i.e., its tail covers its private parts, so too were the warriors of Israel modest and principled during the war with Midian (see Bamidbar 31); i.e., they did not succumb to the temptations of the promiscuous Midianite women.
(Artscroll translation)
Why are "teeth" a reference to "the warriors of Israel"?