To you it was shown, that you might know that the Lord is God; there is no other besides him. Out of heaven he let you hear his voice, that he might discipline you. And on earth he let you see his great fire, and you heard his words out of the midst of the fire.
The way in which God dwelt visibly among Israel in the Penteteuch was meant to bring the people close to Him in faith. They heard the law verbally from God Himself. They saw God lead by smoke and fire in the very center of the camp. God even spoke from that pillar to the people. They had His Word literally sounding out in the very middle of their lives. And yet they struggled with unbelief.
Deuteronomy is a reminder of the Law, a sequel of the covenant in a sermon meant to keep the covenant in mind for Israel. It is Moses' way of ensuring that the nation remembers the Lord. It was given so that between the visible reminders from God every day, and the written words of the Law, Israel would commit in covenant with God.
As always, faith in God among rebel humans who value most our own autonomy is not easy. Israel had God in the camp and His covenant in their hands. Yet they would fail in faith repeatedly, not just in Sinai, but also when they arrived in the Promised Land. We will always quickly forget, which is why we need God's Word to daily remind us as powerfully and as much as possible. I need it. I need a scripture saturated life. I need a daily reminder.