What God stated in Horeb at the base of Mount Sinai, He repeats here. He doesn’t do so because He forgot what the commandment was, but because He wants to make sure the people understand exactly what the covenant is.
To do that, He starts with the decalogue. The phrase “ten commandments” comes from Deuteronomy 4:10, and sums up the entirety of the Law. Even though there are nuances that the people will need to understand, even a basic understanding of these words will serve the people.
Their importance is seen when the Rich Young Ruler visits Jesus and asks what he needs to do to inherit eternal life. Jesus tells him to “keep the commandments;” when the ruler asks which ones, Jesus responds with five of the Ten Commandments (the sixth one in Matthew 19 is a summation of the Law and found in Leviticus 19:18).
The rich young ruler understood that by keeping the Decalogue, he was essentially keeping all of them. That’s why Moses starts with them here: If they can keep these ten, everything else will flow out of them.
But Moses doesn’t just launch into the Ten Commandments. Instead, he begins by repeating God’s initial statement: “I am the Lord your God who brought you out of the land of Egypt, out of the house of slavery.”
That sentence—which most of us gloss over, if we’re being honest—is powerful.
For starters, it teaches us that God’s view of Egypt was literally as a “slave barracks.” Because Israel had a tendency to look favorably at their time in Egypt, moaning about “how good they had it,” God reminds them that it really was nothing more than a house of slaves.
Second, and more important, God affirms what He has done for them. He brought them out of captivity; in saying that, He negates everything other gods have done.
In God’s mind, He was the One who broke into a veritable fortress, filled with all sorts of earthly deities, and liberated His people who were being held as slaves.
That demands respect. It’s why He is able to say “I am the Lord your God”—not just because that’s who He is (although it is who He is), but because He earned that title.
It’s similar to Philippians 2, when Paul says that because Jesus came and died for our sins, God highly exalted Him and “bestowed on Him the name which is above every name.” Jesus is Lord, not only because He is God, but because He earned that title.
Taken in that view, idolatry isn’t just a sin; it’s a slap in the face to Jehovah. Why should a statue of iron get the glory due God? What did it do? Why is it special?
By starting off the Ten Commandments with a very clear understanding of the authority behind the words, the people stand at attention. This isn’t just God speaking—this is their God.