Boy does this section start out dire. God shows Amos a series of visions, beginning with locust infestation and consumption by fire. Amos pleads for Israel's sake. God relents. But then God says he will turn his face against Israel. They will be taken into exile and their king slaughtered. Amos gets busted by the temple priest for prophesying against the king, and responds with more prophecy - specifically against the temple priest. Then there is more prophecy about the inevitability of God's judgment.
The book ends on a hopeful note. God promises that Israel will reclaim its land and never again be uprooted. There will be abundance of harvest and a general contentment.
Several amazing truths are stated in this section. First of all, God is forgiving and can be lenient. Second, when punishment eventually comes, it may not be pretty. Third, don't tell prophets not to prophesy. Finally, God will eventually raise up and bless those who are faithful to him.