Génesis 15:13 Comentario: Rashi, Chizkuni, Da'at Zekenim & Ramban

כי גר יהיה זרעך THAT THY SEED SHALL BE A STRANGER — From the birth of Isaac until Israel left Egypt was a period of 400 years. How so? Isaac was 60 years old when Jacob was born, and Jacob when he went down to Egypt himself stated, (Genesis 47:9) “The days of the years of my sojournings are a hundred and thirty years”, making together 190 years. In Egypt they were 210 years — corresponding to the numerical value of the word רדו (see Rashi in Genesis 42:2) — making altogether 400 years. If, however, you say that they were in Egypt 400 years — well, Kohath was one of those who went down to Egypt with Jacob; go and add up the years of Kohath (130), those of Amram (137), and the 80 years that Moses was old when Israel left Egypt, and you only have about 350, and you really have to deduct all the years that Kohath lived after Amram was born, and those that Amram lived after the birth of Moses (Megillah 9a).

ידוע תדע, G-d used the same words when punishing Avram that Avram had used when asking a question which was sinful. His descendants were ordained to endure exile as an example of matching the punishment to the crime. (Compare Tanchuma Kedoshim, 13) [only according to the exegetes who interpreted Avram’s question as demonstrating doubt in G-d’s promise. Ed.]

ועבדום, וענו אותם, “they will serve them; and they (the masters) will oppress them.” This was the answer to Avraham’s question: במה אדע כי אירשנה, “how will I know that I will indeed inherit it (the land) even vicariously,” in verse 8, where Avraham asked for some kind of guarantee that G–d’s promise to him would not be negated by his descendants forfeiting their claim to its fulfillment.