The prophet Amos spoke out against the injustices of the Northern Kings of Israel. He set the tone for centuries of prophetical figures in Judaism, Christianity, and Islam.
A central theme of the prophetical tradition is social justice. Read Amos 2:6-16; 5:14-15 in this regard (see the Webliography for an online Bible).
Do you think churches have done enough with regard to social inequality, poverty, injustice, and so on? What one issue do you think churches should address today?