במדבר, פרק ג׳, פסוק ד׳

The transfer of the priesthood within Aaron's family is marked by a sudden and profound tragedy. The older sons, Nadab and Abihu, experience a sudden death that comes directly from God, either as a miracle or a divine plague [רמב״ן, הטור הארוך]. The sorrow and divine anger over the loss of these righteous men are immense, even exceeding the deep grief of their own father [צרור המור, דעת זקנים]. Their death is the direct consequence of a single, fatal error: offering a foreign fire before God [ספורנו, ברכת אשר]. In this act, they did not even offer the fire independently; rather, one actively brought the offering while the other simply assisted him [העמק דבר].

A crucial element of this tragedy is that Nadab and Abihu die without leaving any children. This detail dictates the future of the priesthood. In matters of succession, those who are first in inheritance are also first in honor. Had the older brothers fathered sons after being anointed, those children would have naturally inherited the sacred role, bypassing the younger brothers, Eleazar and Ithamar [ספורנו, חזקוני, ריב״א, רש״ר הירש]. Furthermore, dying without descendants makes their passing absolute, as leaving a lineage would have allowed their legacy to live on [תורה תמימה]. The reason they never started families stems from their immense love for the Torah; they avoided marriage to escape the burdens of public life. They also believed that remaining single made them purer and more worthy than their father to enter the Holy of Holies. Had they married and raised families, this sense of superiority would never have taken root, and they would have avoided the tragic sin of the foreign fire altogether [חתם סופר].

Following this devastating loss, Eleazar and Ithamar are elevated by God, receiving authority that extends far beyond their standard duties as Levites [ספורנו, ביאור שטיינזלץ]. Their appointment serves as a form of spiritual redemption for their fallen brothers, who lost their lives on account of the priesthood [שפתי כהן]. Although both younger brothers are deemed worthy of this high honor, the ultimate position of High Priest can only be held by one person at any given time [העמק דבר].

The younger brothers assume their new responsibilities while their father is still alive. The primary approach among commentators is that they function as full High Priests during Aaron's lifetime, stepping in to replace him whenever he becomes ritually impure [רש״י, ביאור שטיינזלץ, שפתי חכמים]. This is not merely the standard service expected of ordinary priests, but rather a rare, historic event where sons are anointed to the High Priesthood while their father, the current High Priest, is still living [רמב״ן, הטור הארוך]. This transition underscores a deeply painful reality, as Aaron is forced to witness both the loss of his older sons and their immediate replacement [רש״ר הירש], with the younger brothers effectively stepping into his eventual place [חזקוני]. Alternatively, this presence alongside Aaron might not refer to the younger brothers' service at all, but rather points back to the initial tragedy, indicating that Nadab and Abihu died directly in the presence of their grieving father [רמב״ן, הטור הארוך, שד״ל, פענח רזא].