One of the many mitzvot appearing in parshat Kedoshim is the prohibition for men against shaving the corners of the hair beyond the temples (pe’ot) and the corners of the beard.
These two prohibitions express ideas fundamental to man’s mission. The hair covering the temples is the externally visible division between the front and the back of the head, and this division coincides with the division between the cerebrum and the cerebellum. The hair at the temples is a natural veiling that hides the view of the back of the head. This division separates the cerebrum — the seat of cognition, representing the human element — from the cerebellum — the center of motor activity, representing the animal element. The division is to remain prominent and we are prohibited from removing it.
Here again we meet the great Torah principle concerning the holiness of life, where the higher dignity of the spiritual element is pronounced. Hair at the temples is found in every human being — in both genders and at all ages. Even the countenance of a newborn is inscribed with this emblem of its moral human mission.
The upper jaw and lower jaw also represent the dichotomy of animal forces and human forces within us. The upper jaw is fixed to the skull and upper part of the face, including the eyes, ears and nose. It relates more to the intellectual activity of the senses and plays only a passive part in the act of eating. The lower jaw, by contrast, with teeth and tongue, are actively involved in eating.
Because the male is more inclined to succumb to sensuality, at the age of maturity, when those sensual faculties are developing, he grows a beard. The beard covers those parts of the face whose primary activity is sensual, and leaves only the spiritual parts of his face — chiefly his eyes and forehead — in full view. This is intended to remind him that in all of his endeavors and activities he is to show his spiritual face and not his animalistic one. The sensual elements of his nature are to be subordinated, hidden. Man is therefore warned not to remove this veil of hair that serves as an ever-present reminder of where his true worth lies.
Women, by contrast, do not grow hair on their face. Because they are less prone to forfeiting their human dignity to the snare of sensuality, they do not need the same reminder. Instead, the men bear the national mark of the human mission on their heads.
§ Sources: Commentary, Vayikra 19:27