God is all about relationships. Deuteronomy seeks to move the hearts of the people into closer relationship with God. God is the one who saves them. God is the one who has grace when they fall. God is the one who leads and guides them. God provides, and God restores.
And yet, when difficulties came, Israel was quick to turn against God and blame Him for the difficulties. At that point, it was much easier for them to listen to others than to God. As noted in Deuteronomy 1, they gave in to fear instead of remembering the mighty works God had already done for them in the past. Not only that, even sending the spies showed a lack of faith. And though Moses and the two faithful spies were speaking encouraging words, the people instead chose to focus on the negative and discouraging words.
Israel had already been through two covenant ceremonies in the past year and had broken both of them (not going up on the mountain in Exod. 19; golden calf incident in Exod. 32). This would be the equivalent to God being jilted for another lover on two occasions. And God had even wanted to start over with a new people (Exod. 32:9-10). Yet He chose to forgive and hope that real change would happen. But instead, the relationship resulted in even more affairs, and even greater betrayal. God is a personal being, whose heart is broken when His people choose to reject Him who loves them so deeply.
It is easy to look at Israel in their continued and recurring horrific choices and wonder how they could come to such a place after God had done so many miracles for them. But this is the condition of the human heart; we naturally prefer death to life, and we prefer to doubt and fear instead of trusting in the God who made us and delivered us. And when we are in a new trial, it is easy to forget the past deliverance. Moses reminds the people of all the times God has delivered them, not to berate them but so that they are less likely to forget in the future when another trial comes.
This is why the middle part of Deuteronomy, the next section of the covenant, fleshes out each of the Ten Words (the Decalogue is never called “commandments” in Hebrew; Moses calls them the Ten Words) in more detail. Since the people had continued to keep their hearts away from God and refused to listen to His voice, God gave them many examples of what their lives would look like when their hearts were in tune with His. Then the covenant ends with blessings and curses, which were a normal part of covenants as well, reiterating the choice that the people needed to make between life and death.