Sarah’s dramatic demand to expel Hagar and Ishmael stems not from a typical family conflict, but from a profound vision for the future of the nation and a deep need to protect Isaac both spiritually and physically. She recognized that Ishmael’s mocking behavior masked severe transgressions, including idolatry, forbidden sexual relations, and bloodshed [כלי יקר, אלשיך, שפתי כהן]. Her primary fear was that Isaac would learn from these wicked actions. While one might assume Isaac could positively influence his older brother and guide him toward a better path, Sarah knew through prophecy that Ishmael would never adopt Abraham’s righteous ways, leaving the educational danger fully intact [כלי יקר].
Beyond the immediate spiritual threat, Sarah opposed any closeness between the two boys. She did not want them growing up under the same roof, forming a friendship, and viewing themselves as brothers [ביאור שטיינזלץ]. Ironically, the absence of an active struggle over their father's legacy might have drawn them closer, making it entirely too easy for Ishmael to corrupt Isaac [פרדס יוסף]. The demand for expulsion included Hagar for several practical and fundamental reasons. On a practical level, a young man could not be sent away without his mother to care for him, and she naturally would not have remained behind [רד״ק, ביאור יש״ר, ביאור שטיינזלץ]. More fundamentally, Hagar was the one who advised Ishmael to disrespect and slander Isaac in order to seize the entire inheritance [ספורנו, מלבי״ם]. There was also a real concern that Hagar would raise her son to avenge the suffering Pharaoh once endured on Sarah’s account [שפתי כהן].
The expulsion was meant to be more than just physical distance; it was a complete legal severance. Sarah demanded that all ties to the household be cut, ensuring they would leave with the definitive status of a maidservant and her son, possessing no future rights or connections [רש ר הירש]. When addressing the issue of the legacy, Sarah was not driven by petty jealousy. She understood Ishmael’s wild and violent nature, realizing that if he remained in the home, he would never settle for a fair division of property. Instead, he would forcefully seize everything, leaving nothing for Isaac [הכתב והקבלה]. Ishmael already considered himself an equal [רד״ק] and even demanded a double portion as the firstborn [חזקוני]. Therefore, a public expulsion during Abraham’s lifetime was essential to clarify to the world, and to prevent any future claims, that Isaac was the sole and true heir [העמק דבר, בכור שור]. Furthermore, the concept of inheritance in this context also carries the meaning of leadership and authority, establishing that Ishmael would never become a ruler over Isaac [הכתב והקבלה].
Sarah emphasized her point by drawing a sharp distinction regarding Isaac's identity, presenting two separate arguments for why Ishmael could not share the legacy. First, Isaac was her son, the child of the primary wife, as opposed to the son of a maidservant. Second, he was specifically Isaac, the miraculously born child, the treasure of the world, and the one with whom God established His covenant [מלבי״ם, ביאור יש״ר, רד״ק]. The primary approach among commentators understands this dual emphasis as a logical progression. Simply being the son of the primary wife, even if he lacked exceptional righteousness, would have been enough to prevent Ishmael from sharing the legacy. Conversely, if he were as righteous as Isaac, even without being the primary wife's son, it would still be improper for the wicked Ishmael to inherit alongside him. Because Isaac possessed both of these profound merits simultaneously, Ishmael's exclusion was absolute.