Amos 1: the Lord is against nations around Israel/Judah.

Amos was a sheepherd in Takoa, Judah. He received a message from the Lord concerning Israel when Israel was doing fine economically in times of Jeroboam II. Reading the Old Testament, we see that the Lord loved Israel despite its idolatry.
We read:

2 The Message:
God roars from Zion,
    shouts from Jerusalem!
The thunderclap voice withers the pastures tended by shepherds,
    shrivels Mount Carmel’s proud peak.

The temple is in Jerusalem, Judah and the Lord shouts from there. His voice can be heard in distant places such as Mount Carmel in Israel.
The Lord is against Damascus, Gaza, Tyre, Edom and Ammon. They mistreated the people of the Lord. For instance Gaza turned Israelites as slaves and sold them to Edom:

6-8 God’s Message:
“Because of the three great sins of Gaza
    —make that four—I’m not putting up with her any longer.
She deported whole towns
    and then sold the people to Edom.
For that, I’m burning down the walls of Gaza,
    burning up all her forts.
    (...)

One application of this text is that the Lord knows I belong to his people. Although I may be mistreated by others (because I belong to Him), I believe that the Lord is taking care of me. Eventually, He will deal with those that mistreated me.