Rashi: They served as testimony that the well belonged to Avraham. The real proof however, lay in the fact that, following the dispute between the shepherds of Avraham and those of Avimelech, after putting it to the test, the water rose to meet Avraham.
2.
Seforno: They came to seal the agreement between the two parties, following Avimelech's admission that Avraham's shepherds had dug the well.
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3.
Rashbam #1: Whatever Avraham intended to achieve, Hashem swore that, as a result of the gift (which Avraham was not authorized to give), Avimelech's descendents would fight seven wars with his descendents, and win.
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Rashbam #2: They would kill seven of his righteous descendents.
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5.
Rashbam #3: That they would destroy seven Mishkanos.
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Rashbam #4: They would capture the Aron, which would remain in 'the Field of the Plishtim' for seven months.
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Targum Onkelos and Targum Yonasan: The gift would serve to induce Avimelech to attest to his (Avraham's) having dug the well.
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Moshav Zekenim: People always take sheep to the well, to drink. People would ask about them, and the shepherd would say that they testify that it is Avraham's well. He gave females, which people retain (for babies; the males they slaughter) - seven, because "Shiv'ah" resembles the word "Shevu'ah".
Much in the same way as we find in Rus (4:7), where 'One man took of his shoe and gave it to his friend' - to substantiate the agreement between Bo'az and P'loni Almoni.
Hadar Zekenim: The Pelishtim later killed seven of Avraham's descendents due to the Bris that Avraham entered into with Avimelech. (Also refer to 22:1:1:4, refer to 22:1:2:1).
QUESTIONS ON RASHI
3)
Rashi writes: "'Tihyeh Li' - this one." What it Rashi clarifying?
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Gur Aryeh: The word Tihyeh can be either second person masculine (meaning, 'you [Avimelech] will be a witness'), or third person feminine ('it will be a witness'). Rashi tells us that the second translation is correct.
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Gur Aryeh: As proven by the word "Edah," which is in feminine.
4)
Rashi writes: "The waters arose to greet Avraham." How did Avraham rely on such a miracle occurring?
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Gur Aryeh: The spring was presently under Avimelech's control, but it was not flowing abundantly, as a spring ought to. Avraham realized that this was because it was stolen property, which is unfit for blessing.
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Avraham was sure that when he approached, it would return to its usual flow.
Rashi writes: "The waters arose to greet Avraham." But perhaps Avraham proved his case through more conventional proof, or through witnesses?
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Mizrachi, Gur Aryeh: The verse says that the sheep themselves were the proof. The waters would not arise without a need; it rose for Avraham's sheep to allow them to drink. Avraham gave those same sheep to Avimelech, as a tangible reminder.
