2Do you not know that the saints will judge the world? And if the world will be judged by you, are you unworthy to judge the smallest matters?

3Do you not know that we shall judge angels? How much more, things that pertain to this life?

The Christians who have have a case against each other should not go to secular court because then it would the unrighteous judging the saints (righteous in Christ). Paul states that the Church is to judge and rule over all things with Christ when He return and now is the training in preparation for that.

Therefore, this matter should have been brought before the Church leadership to judge righteously according to Biblical principles (even those that we have just been looking at).

7Now therefore, it is already an utter failure for you that you go to law against one another. Why do you not rather accept wrong? Why do you not rather let yourselves be cheated?

8No, you yourselves do wrong and cheat, and you do these things to your brethren!

They are actually performing unrighteousness by taking the matter to secular court and hurting their brothers in Christ whereas it would be better for them to let themselves be cheated and not retaliate!