In Brit Bein HaBtarim, God tells Avraham "You shall surely know that your seed will be strangers in a land that is not theirs, and they will enslave them and oppress them, for four hundred years.” (15:13)
What terrible sin did Am Yisrael commit that they were sent into a long, hard exile in “a land that is not theirs”?
The answer is connected to Avraham’s earlier question to God “How will I know that I will inherit it?" (15:8) Avraham does not doubt at all that he will inherit the Land, he only wishes to find out how he will know that he will inherit it forever, that he will not lose it even if Am Yisrael are sent into exile. God’s paradoxical answer, ”You shall surely know that your seed will be strangers in a land that is not theirs” is His reply to Avraham’s question.
God is telling Avraham that his descendants will not be fruitful and multiply in the Land of Israel in the natural way, like all other nations. If Am Yisrael’s connection to the Land would only be a natural one, then there is a danger that the connection would be severed as a result of exile, as happened to other ancient nations. Therefore, Am Yisrael must develop as a nation in a land that is not theirs, in an unnatural manner, and only God Himself will take them out of exile to freedom to the Land that He has chosen for His people.
We can now understand that the first exile in Egypt was not a punishment for sins committed by Am Yisrael but rather it served the purpose of molding and building the future nation. The Land of Israel is not just a homeland, but is the Land chosen by God where Am Yisrael will fulfill its destiny.