There's a
summation here
The overall message is threefold:
Deuteronomy stresses the uniqueness of God (Yahweh), the need for centralisation of worship (the Temple at Jerusalem) and a concern for the position of the poor and disadvantaged.
The core of Deuteronomy is the covenant that binds Yahweh and Israel by oaths of fidelity and obedience. God will give Israel blessings of the land, fertility, and prosperity so long as Israel is faithful to God's teaching; disobedience will lead to curses and punishment. The First Commandment is "Thou shalt have no other gods before me." The Shema Israel (6:4-5) is a repetition of that.
"Because the Lord thy God is a jealous God in the midst of thee: lest at any time the wrath of the Lord thy God be kindled against thee, and take thee away from the face of the earth." (6:15).
"But if thou forget the Lord thy God, and follow strange gods, and serve and adore them: behold now I foretell thee that thou shalt utterly perish. As the nations, which the Lord destroyed at thy entrance, so shall you also perish, if you be disobedient to the voice of the Lord your God." (8:19-20)