The distinction between the sexes is a fundamental pillar of the created order. Maintaining the unique identity, nature, and role of men and women is not merely a matter of social convention, but a profound spiritual and moral directive. Blurring these boundaries leads to moral decay and undermines the specific purpose God granted to each individual. The primary approach among commentators is that the practical and central reason for maintaining this separation in dress is to prevent adultery and prostitution. When individuals dress in the clothing of the opposite sex, they can blend into crowds unrecognized, paving the way for secret transgressions [רש״י, רשב״ם, אבן עזרא, בכור שור, רלב״ג]. This separation also prevents disguises intended for homosexual acts or other forbidden relationships [שפתי כהן, אברבנאל]. Because the ultimate concern is the prevention of acts that lead to promiscuity, the directive concludes by labeling such behavior an abomination [רש״י, תורה תמימה].
A careful distinction is made regarding what is forbidden to each sex. For a woman, the restriction focuses on carrying the gear of a man, which primarily refers to weapons and armor. Historically and practically, warfare is the domain of men, and it is contrary to a woman's nature to go into battle. Entering a military environment exposes a woman to surroundings that could easily lead to moral compromise and prostitution [אבן עזרא, רבנו בחיי, חזקוני]. This principle is historically illustrated by Yael, who killed the Canaanite general Sisera using a tent peg and a hammer rather than a sword, specifically to avoid the prohibition of carrying a weapon [רבנו בחיי, הדר זקנים, צאינה וראינה]. Beyond weaponry, some expand this concept to include ritual items uniquely designated for men, such as tzitzit and tefillin [מלבי״ם, קונטרס חיבה יתירה].
Conversely, the restriction for a man centers on wearing a woman's garment, which implies fine, decorative clothing made for adornment [מלבי״ם, תורה תמימה]. This goes beyond literal clothing and encompasses the adoption of grooming and beautification habits distinct to women. Men are forbidden from dyeing their hair, plucking white hairs from among the black, removing body hair in areas where only women typically do so, or even gazing into a mirror for the sake of vanity, unless required for medical reasons [רש״י, רבנו בחיי, תורה תמימה, ביאור יש״ר].
On a deeper level, these guidelines are designed to preserve the distinct strengths and traits God bestowed upon each sex. Men and women are meant to actualize their unique potential without attempting to imitate the nature of the other. When a woman feels compelled to adopt masculine mannerisms, it implies a mistaken belief that femininity is inferior and must compete with masculinity. Instead, the Torah deeply cherishes femininity and encourages women to cultivate their distinct abilities [רש״ר הירש, חומש קה״ת]. Psychologically, while changing clothes is an immediate action, altering one's nature is a gradual process. There is a warning against habituating oneself to the customs of the other sex, as this routine eventually leads to a complete external transformation and forbidden mingling [העמק דבר].
Historically, cross-dressing was a widespread practice in ancient idolatrous cults. Pagan priests would wear women's garments, and women would don armor during rituals that were frequently accompanied by severe promiscuity. The Torah seeks to entirely uproot any remnant of these corrupt practices [אם למקרא]. Beyond the literal meaning, there are moral and spiritual allegories woven into this directive. A man is cautioned against adopting a posture of weakness or softness in order to shirk the responsibility of helping others with heavy burdens, or to lazily avoid the effort required in Torah study [אברבנאל, פני דוד]. Finally, according to Kabbalistic thought, man represents the spiritual concept of the giver, while woman represents the receiver. Swapping garments reverses these roles, disrupting the foundational order of creation and damaging the spiritual framework of the world [שפתי כהן].