Forbidden intimacy within the family carries severe consequences, both spiritual and practical. A strict boundary is drawn against relations with an aunt, specifically the wife of an uncle. In biblical law, this relationship refers exclusively to the wife of a father's brother, whereas the wife of a mother's brother is restricted only by later rabbinic decree [תורה תמימה, מלבי״ם, אדרת אליהו].
A fascinating distinction exists between the prohibition of marrying an aunt and the permission to marry a niece. In a traditional marriage, a husband naturally holds a position of authority over his wife. Marrying an aunt would inherently compromise the respect she is owed and diminish her standing within the family hierarchy, which is why the relationship is forbidden [תיבת גמא, פרדס יוסף]. Additionally, in ancient times, there may have been a custom for a nephew to marry his deceased uncle's widow to carry on his legacy. Therefore, it was necessary to absolutely prohibit this practice, penalizing it with the complete erasure of the sinner's own name [רד״צ הופמן].
The penalty for this act is a tragic one: dying childless. This represents a state of deep historical loneliness, where a person's time on earth ends without leaving any continuity behind [רש״י, אבן עזרא, רש״ר הירש]. The primary approach among commentators is that this specific consequence serves as a template to explain the severe heavenly punishment of being spiritually cut off, which applies to all forbidden sexual relations. It reveals that this penalty is not merely a shortened life for the sinner, but also the cutting off of their future lineage [רש״י, מזרחי]. However, this tragic loss of offspring applies only to young children who have not yet established their own independent merit, rather than adult children who are judged on their own actions [שפתי חכמים, גור אריה]. Ultimately, Divine providence ensures that the sinner will not leave any living descendants [רשב״ם].
A careful look at the surrounding laws reveals a subtle distinction. While the penalty here is described as dying childless, a subsequent law regarding a brother's wife describes the sinners as remaining childless. Together, these two expressions cover all possible scenarios of the punishment. If the individual already had children when the sin was committed, he will tragically bury them during his lifetime and die alone. Conversely, if he had no children at the time of the act, he will remain in that state and never have offspring before his death [רש״י, תורה תמימה, שפתי חכמים].