Deuteronomy is the final book of the Torah (the first five books of the Bible). It takes place on the plains of Moab, just before Israel enters the Promised Land.
The first generation rescued from Egypt has died in the wilderness because of unbelief. Moses now addresses a new generation who are about to inherit God’s promises. Moses himself will not enter the land. These are his final words, sermons given to prepare God’s people for life with him in the land.

Deuteronomy is not a “new” or “second” law in the sense of changing God’s commands. It is the re-preaching and re-applying of God’s word for a new moment, calling God’s redeemed people to trust him and live faithfully.