Amos comes to warn God's people that their excessive and continuous sinfulness has brought upon them God's judgment.
He begins by telling that God will punish the heathen nations surrounding Israel & Judah for their treatment of God's chosen. He then turns his attention to Judah and Israel (largely though not exclusively Israel). They were to receive God's wrath because they had scorned and mocked His holy commandments, consistently rejected His warnings and mercy, and become abjectly immoral. Because they had abandoned God, He will now punish them, and nothing can turn this punishment away.
But alas, as always, God will preserve His remnant and after the punishment, will restore to them the Kingdom, even bringing in the Gentile nations. This is obviously a reference to His establishment of the church.