How did God repeatedly remind Israel that they were different from all other nations?
God placed a clear difference between Israel and Egypt: while judgment fell on Egypt's firstborn, not even a dog moved against the children of Israel. From Abraham onward, He constantly reminded them they were not like everyone else on the planet but were distinct. He controlled even the animal kingdom to demonstrate this separation.
Les explains that during the Exodus judgment, God said all the firstborn in Egypt would die, from Pharaoh's firstborn to the maidservant behind the mill and even the livestock, causing a great cry throughout Egypt. But against any of the children of Israel, not even a dog would move. Les notes this shows God is in control of even the wildlife or animal kingdom, and he connects it to Jesus telling Peter to find tax money in a fish. The purpose in verse 7 was that Israel might know the Lord puts a difference. Les says he repeats himself so these things sink in, and all through Israel's history from Abraham, God constantly reminded them they were not like everybody else but were different.