Q. In the beginning of the Egyptian servitude at the start of Sefer Shemos, Rav Sa'adya Gaon (see Rav Kapach's translation in Chumash Toras Mosad Rav Kook) says that "Ka'asher yianu oso...kain yifrotz"' means that Kal Yisroel became wealthy. What good would wealth do for an enslaved nation?
A. I did not find the peirush of Rav Sa'adia Gaon you quoted, but I did find something similar in the Hagada Be'er Chaim Mordechai (p. 103,) and in Misgav Ledavid (P. Shemos). The Jewish nation merited their wealth when leaving Mitzraim by the virtue of Avraham Avinu, whom Hashem blessed with abundance (V'avorechecha - bemomon). The term used for the suffering imparted to them by the Egyptians is “Vaya'anu” which is an expression of poverty; they desired to impoverish and deprive them, but the result was exactly the contrary. The enslaved became exceedingly wealthy, when they deprived their tormentors and took all their riches. The word “Yifrotz” links with “Vayifrotz haish meod” (Bereshis 30: 43.)
It is obvious, that this enrichment was only after they left Egypt with the “rechush gadol”
Horav Shlomo Millers Shlit”a mentioned that although the Bney Yisroel were enslaved, they did posses and own cattle which traditionally has been an important source for wealth. The Talmud (Chulin 84a) mentions that Rabbi Yochanan taught: "Anyone who wants to get rich should engage in the raising of sheep." Rabbi Chisda added: "Why are flocks of sheep referred to by the Torah as ashteroth zonecho? (Devarim 7:13) Because sheep enrich their owners."
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a