Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices—mint, dill and cummin. But you have neglected the more important matters of the law—justice, mercy and faithfulness. You should have practiced the latter, without neglecting the former. (Matthew 23:23)
God is a God of justice, mercy and faithfulness. And yet, we cannot sit idly by and wait for Him to bring these about.
What, you mean we have to do these great works instead of God?
No, not at all. I mean we have to do these great works because of God. Because God is a God of justice, mercy and faithfulness, we are called (quite specifically) to live out those three principles in our own life. Don't forget that God often does His great works through His children. (Thus it is that Works do not get us saved but rather are a natural outpouring of the fact that we are.)
So if you see someone being treated unjustly, instead of saying "someone should do something," perhaps you should say "God what do you want me to do?" And then live it out.