Through Moses, God commanded the Jews to construct 2 memorials when they arrived in Canaan (or maybe just 1 edifice that would serve 2 purposes - Deuteronomy 27:7 & 8). They were required to make a monument with the 10 Commandments written on it and they were supposed to build an altar. Maybe the 2 were one and the same. Either way, once that task (or those tasks) was (or were) done, the Levites were to pronounce a great curse over the people (to which they were to heartily agree). Actually, 6 tribes were to antiphonally respond to the curse and the other 6 were to respond to an equally important blessing.
Here are the sins that would specifically bring swift cursing from God. Idolatry, disobedience to parents, dishonesty with a neighbor, unconcern about the handicapped, dishonesty with the downtrodden, sexual impurity, wicked violence, acceptance of bribes and... well, just rebellion in general - all of those bad behaviors were dangerous in that God would curse the guilty. And, the people were required to avouch for His word in that regard with many a hearty "Amen!"
Now, more of the same will be found in the next chapter. And, both the blessing and cursing were used by God to motivate the people toward righteousness. Let us never neglect the reality of God's curses. They are as real and as powerful as His blessings.