First Letter to the Corinthians 6,1-11. 
When any of you has a grievance against another, do you dare to take it to court before the unrighteous, instead of taking it before the saints?
Do you not know that the saints will judge the world? And if the world is to be judged by you, are you incompetent to try trivial cases?
Do you not know that we are to judge angels to say nothing of ordinary matters?
If you have ordinary cases, then, do you appoint as judges those who have no standing in the church?
I say this to your shame. Can it be that there is no one among you wise enough to decide between one believer and another,
but a believer goes to court against a believer and before unbelievers at that?
In fact, to have lawsuits at all with one another is already a defeat for you. Why not rather be wronged? Why not rather be defrauded?
But you yourselves wrong and defraud and believers at that.
Do you not know that wrongdoers will not inherit the kingdom of God? Do not be deceived! Fornicators, idolaters, adulterers, male prostitutes, sodomites, thieves, the greedy, drunkards, revilers, robbers none of these will inherit the kingdom of God.
And this is what some of you used to be. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and in the Spirit of our God.

"the saints will judge the world": let's hope that st. Paul and his friends will judge us well and will say a good word to defend us one day.

"a believer goes to court against a believer and before unbelievers": Paul tries to let us wake up, also and especially today, after 2000 years. It reminds me of the married couples, who married in church, but when they face problems, they seek for an advice by an unbeliever lawyer that works with divorces. It's not a clever idea. Paul is repeating it today, and he doesn't get tired to repeat it.