Before the Israelites went in to take possession of the Promised Land, Moses was determined to reiterate the law the Lord had given them. In fact, the very name of this book means a "second" (deutero) giving of the "law" (nomy). Remember, this was 40 years after God had originally given the law to the Israelites at Mount Sinai, and those who were now in Moses’s audience were either babies at that time or not yet born.
Obviously, God gave us the law because He wants us to obey. But when Jesus was asked about which was the greatest "rule," He said this: "'Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment. And the second is like it: 'Love your neighbor as yourself.' All the Law and the Prophets hang on these two commandments." (Mt 22:37-40) What Jesus was saying was that love is the greatest commandment... but love isn’t something that can be commanded, is it? You cannot elicit love from a person by threatening them with punishment if they don’t comply.
And that’s precisely the point. Even though God gave the law (because He was beginning with people who needed it spelled out for them), God was essentially asking them to do something that He can’t ultimately command. And that’s why, in verse 29, He explains why He wants this obedience: "Oh, that their hearts would be inclined to fear me and keep all my commands always, so that it might go well with them and their children forever!"
You see, God is just a good parent who wants to see His children happy and satisfied. That’s why He wants us to obey — not because He demands respect for His authority, but because love is the only thing that will lead us to true happiness, peace, and joy. He wants us to obey for our sakes, not for His sake. He wants us to do the things He can’t command so we will reap the natural consequences of obedience, which are things He can’t bestow.