Why does the Torah mention the slavery in Egypt?
Rashi (on Pasuk 5): Refer to 26:5:3:1. It is one of the things for which the owner of the Bikurim is thanking Hashem.
Seforno: Continuing with the owner's explanation as to why we did not receive Eretz Yisrael earlier, 1 he points out that even after we became a nation, we were not able to establish a nation that could do so, since we became slaves to the Egyptians, 2 and 'Whatever a slave acquires belongs to his master'. 3