Charles Ellicott Commentary Deuteronomy 6:21

"then thou shalt say unto thy son, We were Pharaoh`s bondmen in Egypt: and Jehovah brought us out of Egypt with a mighty hand;" — Deuteronomy 6:21 (ASV)

The Lord brought us out of Egypt. —The simple explanation of the obligations of the Law given in these verses is based upon the message of Jehovah to Israel from Sinai (Exodus 19:3–6): You have seen what I did to the Egyptians, and how I bore you on eagles’ wings, and brought you to myself. Now therefore, if you will obey my voice indeed, and keep my covenant, then you shall be a peculiar treasure to me. The keeping of the Law of Jehovah by Israel as a nation in the land that He gave them was the ultimate reason for their national existence. This fundamental fact must never be forgotten. This alone would justify what had been done to Egypt. Therefore, the neglect of the Law must inevitably bring down Divine vengeance.