How could the money in their sacks have possibly been a mistake?
Rashbam: Perhaps the money was placed on top of the sack as a sign, to know how much each brother had purchased, and they forgot to take it back before they left.
Why did he add the word "Kechu b'Yedchem"?
Oznayim la'Torah: Because the only safe way of guarding money when traveling, is by holding it in one's hand. 1
Ha'amek Davar: The new money is in your Reshus. The returned money "Tashivu b'Yedchem," carry it openly in your hands and return it immediately, before you are asked.
As the Gemara states in Bava Metzia 42a - based on the Pasuk in Devarim 14:25.
What is Kesef Mishneh?
Rashi: It is twice as much as the first time (in addition to the money that was returned 1 ); perhaps the price rose.
Ha'amek Davar: It is what was already returned, as well as new money to buy now (not necessarily double the first amount). 2
Malbim: Yaakov suspected that the money was put in their sacks to test whether or not they are honest.
Gur Aryeh: Why didn't Rashi explain this way? If so, the money being returned should have been mentioned first! Rather, Rashi explains that it means double the original amount (just for purchasing food; in addition to returning the original amount).
QUESTIONS ON RASHI
Rashi writes: "Perhaps it is a mistake - Perhaps the overseer of the house forgot it by mistake." Isn't it possible that the brothers themselves had made the mistake?
Gur Aryeh: In a purchase, it is not the buyer who seeks to give over the cash, but rather the seller who demands it. If the money did not change hands, it was the seller's mistake.
