בראשית, פרק ל״ח, פסוק ח׳

When a father instructs his son to marry his deceased brother's widow to ensure the continuation of his line, it reveals a practice steeped in ancient tradition and profound spiritual mystery. The primary approach among commentators is that this custom, known as levirate marriage, was a recognized law long before the Torah was given [רד״ק, אם למקרא]. It is deeply connected to the spiritual rectification of the human soul. By providing offspring, the marriage serves as a redemption for the deceased brother, restoring his soul and preventing his spiritual source from being permanently severed [רמב״ן, רקנאטי].

The application of this custom evolved significantly over time. In antiquity, any close relative, such as a father or extended family member, could marry the widow to benefit the soul of the departed. Later, the Torah restricted this practice exclusively to paternal brothers, ensuring the commandment could be fulfilled without violating other severe prohibitions against incest [רמב״ן, ביאור יש״ר, חזקוני]. Judah's instruction marked a pivotal shift in this tradition. He was the first to transform levirate marriage from an optional act of compassion into an absolute family obligation. Because Onan was forced to perform this duty against his will, he chose to secretly waste his seed [מזרחי].

The precise nature of Judah's directive to his son carries several layers of meaning. On a basic level, it was a straightforward command to step into the role of the brother-in-law and fulfill the duty of marriage [אבן עזרא, אבי עזר, מלבי״ם]. It can also be understood as an instruction to actively remove the woman's agonizing status as a waiting widow through the act of marriage [חזקוני, מחוקקי יהודה]. Beyond the legal obligation, the directive served as a strict moral warning. Judah cautioned Onan to approach his brother's widow solely for the sake of fulfilling the commandment, rather than for physical pleasure, ensuring he would not stumble into sin as his brother had [אלשיך]. Another perspective suggests the duty required only a single intimate act to fulfill the commandment, even if Onan intended to divorce her immediately afterward—a minimal requirement he still refused to meet [העמק דבר].

The ultimate goal of this union was to raise offspring for the deceased brother, a concept that sparked a fascinating debate regarding how the child would memorialize the dead. An early interpretation suggested the newborn would literally be given the deceased brother's name. However, [רמב״ן] strongly disputed this, arguing there is no obligation to use the exact first name, as evidenced by later biblical accounts where children born of such unions received entirely different names. Furthermore, he noted that Onan would not have committed a grave sin and brought ruin upon himself merely to avoid memorializing his brother, an act most people would gladly do.

Instead, a broad consensus clarifies that the concept of the "name" refers to lineage, belonging, and continuity. The child would not be considered Onan's son, but rather the legal and essential heir of the deceased brother, with the biological father serving only as a substitute [שד״ל, הכתב והקבלה, שפתי חכמים, גור אריה, ביאור שטיינזלץ, ביאור יש״ר]. This dynamic perfectly explains Onan's refusal, as he knew the resulting child would never truly belong to him. Alternatively, some suggest that while there is no obligation to use the literal name after the Torah was given, during Judah's ancient era, the prevailing custom was indeed to name the first son exactly after the departed brother [מזרחי, דברי דוד].