Dora Bas Rivka Silver O'H
These are the words of Amos, who owned herds in a place called Tekoa and who was a prophet during the reign of Uzziyahu in Judah and Yeravam (Jeroboam II) in Israel. This occurred two years before an earthquake, which Amos predicted (see Zechariah 14:5 and elsewhere).
G-d will "roar" from the Holy of Holies in the Temple and send His voice from Jerusalem. Dwelling places will be ruined and fertile land will dry up.
The prophet starts with a message about the fate of Damascus. G-d had forgiven three sins of theirs, but he will not forgive the fourth. What was that sin? They thrashed the people of Gilead with iron instruments. G-d will send a fire to consume the land of Aram (the country of Damascus at the time). He will break down the doors that they will use to try to keep their enemies out; the people of Aram will be exiled.
Similarly, G-d has forgiven three sins of Gaza, a city of the Philistines, but He will not forgive the fourth. What was their "final straw?" They assisted Edom in exiling the Jews. (This appears to refer to the Roman exile in the time of the second Temple.) Fire from G-d will consume their palaces and the remnant of their exiles will be lost.
G-d will also forgive three sins for Tzor (Tyre), but not the fourth. Their final sin was that they were allies with Israel and they broke their pact by delivering the Jews into the hands of Edom. In payment for this, Tzor will be burned (either by Nebuchadnezzar or by Alexander - or, possibly, by both).
And what about Edom themselves? Their deal-breaking sin was that they mercilessly persecuted their brother. (Edom's ancestor Esau was the brother of Israel's ancestor, Jacob. The Radak tells us that the sin of Edom refers to the destruction of the second Temple by the Romans.) G-d will send the consuming fire throughout Edom.
The nation of Amon also committed one sin more than G-d was willing to forgive. When they invaded Gilead, they cut open the pregnant women so that there would be no heirs to try and reclaim the land at a later date. They will not only have fire, but also war like a whirlwind. Their royal family will be driven into exile.