1 Corinthians 4:3-5 NKJV
But with me it is a very small thing that I should be judged by you or by a human court. (a) In fact, I do not even judge myself. For I know of nothing against myself, yet I am not justified by this; but He who judges me is the Lord. Therefore judge nothing before the time, until the Lord comes, who will both bring to light the hidden things of darkness and reveal the counsels of the hearts. Then each one's praise will come from God.
(a) court is literally 'day'
NLT says 'authority', CEV says 'court of law'.
The NLT says Paul doesn't trust himself to judge himself. Just because he thinks he's clean, doesn't mean he is.
So it shouldn't really matter to us to be judged by a person or group of people. In this life, something like a court of law's judgement does matter, but all God cares about is His own judgement. He doesn't even take our own into consideration.
My principal told me once that he couldn't leave discipline for cheating and other things up to a council of students, because they would be harsher on a cheater than he would be. We're harsher on ourselves and our peers than authorities are, some of the time, because we see things differently. In the situation with God, He has a clearer head than we do, so He's able to make the judgement for us.
The other side of that is sometimes we forget or 'forget' about a sin. God sees all of our sin. If He hasn't forgiven us for that sin, tough cookies. Just because you forgot about it doesn't mean God won't hold you to it.
Before you get nervous, when a person is saved, all of their sins are forgiven them.
The other part of these verses is that God does the judging, not other groups. When you die, it won't be the popular kids around a table and you have to go up and beg for mercy. It'll be God up there. And you'll already know your fate with Him if you reside in Christ.
In His Service