Check out Colossians 3:22. "Servants, obey in all things your masters according to the flesh; not with eyeservice, as menpleasers; but in singleness of heart, fearing God:"
Often when we talk about this verse in church we make application to bosses and employees, and that is a fair application. However, the Apostle Paul was referencing slavery. This evil of one man owning another was common in his culture. It was neither within Paul's ability nor his calling in life to change the injustice of slavery. His job was to tell both the slave owners and the slaves to behave like Jesus would in their situation. The slave owners he told to be good and gentle. The slaves he told to work and be loyal.
Over the years God would put men into prominent positions of government in many countries to change the injustice of slavery. We have to remember that God works out His plans not in days and weeks, but in decades and generations.
And so, you and I face smaller injustices in our own lives. Things that are just not right. Things that are not fair. Some of these we can change, and we should. Some injustice we should speak out about, and we should. But there are some injustices that we don't have the ability or the calling in life to change. For these unfair situations we must follow Paul's instructions and find a way to act like Jesus in the midst of an unjust circumstance. After all, wasn't the cross unjust?