The Torah establishes strict boundaries regarding family purity and marital unions, ensuring that the foundational relationships within a household remain sacred and unviolated. A son is strictly forbidden from marrying his father's wife, a rule that carries profound legal and moral weight. The placement of this prohibition immediately following the laws concerning a man who forces himself upon a virgin is highly intentional. A sharp contrast is drawn between the two situations: while a father who commits such an act is obligated to marry the woman, a son is strictly warned against taking his father's wife. Yet, this juxtaposition reveals a vital legal distinction. A son is actually permitted to marry a woman his father had previously violated. This is because forbidden family ties that prevent marriage are established exclusively through formal marital rites, not through mere physical acts [אבן עזרא, רלב"ג, הירש].
The specific language used to describe the son's forbidden union focuses on the act of taking or acquiring, rather than the more common expression of uncovering nakedness. This choice conveys a crucial legal principle: formal marriage has absolutely no legal standing in cases of severe forbidden relationships. If a man attempts to formally marry his father's wife, the union is completely void from its inception, and she requires no document of divorce from him to be free [רש"י, מלבי"ם, תורה תמימה]. Furthermore, this strict prohibition remains fully in effect even if the father has died or divorced her [שטיינזלץ].
The prohibition also extends to uncovering the father's protective garment. The primary approach among commentators is that this refers to the widow of the father's childless brother, who is waiting for the father to fulfill the duty of levirate marriage. The imagery of a garment stems from the ancient custom of spreading the corner of one's clothing over a woman as a symbol of marriage and protective shelter, similar to the story of Ruth and Boaz. Because this widow is legally bound to the father, she is considered destined for the shelter of his garment [הכתב והקבלה, מלבי"ם, העמק דבר]. This specific addition places a double prohibition upon the son: he violates not only the standard restriction against marrying his aunt, but also a unique restriction regarding a woman awaiting levirate marriage with his father [רש"י, מזרחי]. Others, however, suggest this imagery refers to a woman the father had previously forced himself upon [אבן עזרא, בכור שור], while some view it simply as a general, poetic metaphor for the father's clothing and the shame of uncovering his nakedness [רלב"ג, שטיינזלץ, ביאור יש"ר].
The repetition of these severe marital prohibitions, which were already outlined in the book of Leviticus, serves to connect them directly to the subsequent laws regarding illegitimate children. This proximity establishes a fundamental rule: an illegitimate child is defined exclusively as one born from a forbidden union that carries the severe divine punishment of spiritual excision, such as the aunt awaiting levirate marriage, or the even harsher court-imposed death penalty, such as the father's wife [רש"י, רשב"ם, ברכת אשר]. Although a law concerning a man with damaged reproductive organs physically separates these topics, it does not disrupt the conceptual flow. Because a man in such a condition is incapable of fathering children, the narrative naturally progresses to discuss the legal status of children born from forbidden marriages [מזרחי, ברטנורא, אלשיך].