Matthew Poole and continuators on Deuteronomy 21:12

12 Then thou shalt bring her home to thine house, and she shall shave her head, and pare her nails .

Either 1. to take off his affections from her by rendring her uncomely and deformed, but then the last words must not be rendred, shall pare her nails, but shall nourish them or suffer them to grow, as the Chaldee, Arabick and divers of the learned Iews and other Interpreters render it. Or 2. to express her sorrow for the loss of her father and mother, as it follows ver. 13. it being the antient custom of mourners in most nations to shave themselves, and in some to pare their nails, in others to suffer them to grow. Or rather 3. in token of her renouncing her heathenish Idolatry and superstition, and of her becoming a new woman, and embracing the true religion. Which her captive condition and subjection to his will would make her inclinable to do in profession.

Marginal references: Or, suffer to grow.; Heb make or dress.