Bava Batra 130B

מה תלמוד לומר: ״לא יוכל לבכר״?

Why must the verse state: “He may not make the son of the beloved the firstborn” (Deuteronomy 21:16)?

לפי שנאמר: ״והיה ביום הנחילו את בניו״. שיכול והלא דין הוא ⁠– ומה פשוט, שיפה כחו, שנוטל בראוי כבמוחזק ⁠– התורה נתנה רשות לאב להנחיל לכל מי שירצה; בכור, שהורע כחו, שאינו נוטל בראוי כבמוחזק ⁠– לא כל שכן? תלמוד לומר: ״לא יוכל לבכר״.

Abba Ḥanan explains: It is necessary because it is stated previously in the verse: “Then it should be, in the day that he causes his sons to inherit,” as one might have thought: Could this not be derived through an a fortiori inference, as follows: And if with regard to an ordinary son, one who is not a firstborn, whose power is enhanced in that he takes in inheritance the property due the deceased as he does the property the deceased possessed at the time he died, nevertheless, the Torah gave the father permission to bequeath his estate to whichever of his sons he wishes, depriving his other sons of their portions, then with regard to a firstborn, whose power is diminished in that he does not take a double portion of the property due his father as he takes of the property the deceased possessed at the time of his death, is it not clear all the more so that his father can deprive him of the double portion he receives as a firstborn? Therefore, the verse states: “He may not make the son of the beloved the firstborn.”

ויאמר ״לא יוכל לבכר״; מה תלמוד לומר: ״והיה ביום הנחילו את בניו״?

Abba Ḥanan continues: And let the verse state only the prohibition of: “He may not make the son of the beloved the firstborn.” Why must the verse state: “Then it should be, in the day that he causes his sons to inherit”?