The intimate moment of a grandfather blessing his grandchildren takes a sudden, dramatic turn. A father watches in dismay as his elder son is bypassed for the younger, prompting a physical intervention to correct what appears to be a grave error.
The primary approach among commentators is that this intervention actually occurred before the grandfather even began speaking, though the narrative groups the spoken blessings together to maintain the flow of the story [רשב״ם, העמק דבר, ביאור יש״ר]. Alternatively, the intervention took place immediately after the blessing commenced [רד״ק]. Initially, Joseph may have assumed his father was attempting to balance the honors between the two boys, granting the younger son the physical prestige of the right hand while reserving the primary verbal blessing for the firstborn. However, once he realized both sons were being blessed equally, it became clear that a complete preference was being shown to the younger brother, prompting him to act [תולדות יצחק, אלשיך].
The distress Joseph experienced stemmed from several deep-seated concerns. Beyond a natural affection for his firstborn [רמב״ן, הטור הארוך], his primary fear was that his father, whose eyesight was failing, had simply made a mistake in identifying the boys. If a blessing is bestowed accidentally and without the proper intention, it lacks divine spirit and will not take effect [רמב״ן, הטור הארוך, צאינה וראינה]. Joseph also carried a sense of personal guilt, worrying that his own placement of the boys had confused his father into thinking the firstborn was standing on the left [העמק דבר]. Furthermore, he felt personally slighted, as though his father viewed him as foolishly incompetent at properly presenting his own children [רשב״ם, הדר זקנים, דעת זקנים].
On a deeper psychological level, Joseph's reaction was rooted in his own traumatic past. Having suffered immensely from brotherly jealousy sparked by his own father's favoritism, he was terrified that showing preference to the younger brother would plant the same destructive seeds of hatred between his own sons [קונטרס חיבה יתירה, אלשיך]. Additionally, some suggest Joseph possessed a prophetic intuition that the wicked King Jeroboam would eventually descend from the younger son, a realization that deeply troubled him [שפתי כהן].
To correct the situation, Joseph physically intervened, though he did so with profound gentleness and respect for his elderly, frail father. Rather than forcefully moving the hand away, he supported it from underneath to slowly and carefully guide it off the younger son's head [העמק דבר, ביאור שטיינזלץ, ברכת אשר על התורה]. Practically, he lifted the hand and held it in the air to prevent it from falling back into its previous position [רש״י, מזרחי, שפתי חכמים, גור אריה]. His ultimate intention was a single, continuous motion: to gently remove the hand from the younger brother and carefully lay it upon the head of the firstborn, restoring the natural order he believed was intended [רשב״ם, הכתב והקבלה, ביאור יש״ר, רלב״ג].