I think one of the biggest errors we make in reading the book of Deuteronomy is ascribing the things we read to the generation that left Egypt. They’re not. That generation—everyone over the age of 20 during the Exodus, at least—died in the wilderness.
By contrast, this generation was a bunch of children during those events (if they were even alive yet, that is). That means they still saw the effects of God’s discipline even if they weren’t necessarily the ones guilty of the crimes.
That’s what God wants them to remember. To drive that point home, though, Moses gives them four different perspectives of His power that they would do well to remember.
The first one is the discipline given to Pharaoh. Jehovah destroyed the Egyptian gods on their own turf (“in the midst of Egypt”), which is key. Most ancient pagan religions favored regional gods who owned and protected their lands. Moses’ statement here is akin to saying God invaded and destroyed Egypt from the inside out.
The second round of punishment was inflicted on Pharaoh’s army, which was destroyed at the Red Sea. The Hebrew here literally translates “completely destroyed them” as “to this day,” implying that Egypt still hasn’t recovered militarily from that event, now forty years in the future.
Thirdly, the punishment came to Israel (Deuteronomy 11:5). They were punished after the spies’ bad reports and after the golden calf, among other infractions (Deuteronomy 9:22).
Last, they should never forget what happened to Dathan and Abiram, the co-conspirators with Korah, who fell into the earth as it opened up to swallow them (Numbers 16). That would stick with anyone.
It’s a recurring theme in Deuteronomy for Moses to emphasize personal experiences to reinforce devotion. It can’t shape doctrine; that’s what the Law was for. But it certainly can remind us who it is that we serve.