You will hear it often. They are quoting Matthew 7:1 “Judge not, that you be not judged.” The word judge comes from a root meaning “to bring to light.” In my 42 years of experience I can guarantee you the people who parrot this have something in them they do not want brought to light.
The Bible has a lot more to say about judging than one verse. It also says 1 Corinthians 5:12 For what have I to do with judging those also who are outside? Do you not judge those who are inside?
Clearly we are supposed to know those who call themselves Christians and are part of the faith. Unfortunately we see churches judging outsiders (not allowed) and giving a quick pass to fellow members.
God says He will judge those who are non-believers.
Here is what The Message says – a slangy version of verses
9-13 I wrote you in my earlier letter that you shouldn’t make yourselves at home among the sexually promiscuous. I didn’t mean that you should have nothing at all to do with outsiders of that sort. Or with crooks, whether blue or white-collar. Or with spiritual phonies, for that matter. You’d have to leave the world entirely to do that! But I am saying that you shouldn’t act as if everything is just fine when a friend who claims to be a Christian is promiscuous or crooked, is flip with God or rude to friends, gets drunk or becomes greedy and predatory. You can’t just go along with this, treating it as acceptable behavior. I’m not responsible for what the outsiders do, but don’t we have some responsibility for those within our community of believers? God decides on the outsiders, but we need to decide when our brothers and sisters are out of line and, if necessary, clean house. (emphasis mine)
This is why we encourage intervention. But we are cowards aren’t we. This is God’s will for church folk. And if you are guilty of telling people not to judge you, examine yourselves to see if you are walking in the light. 2 Corinthians 13:5 Examine yourselves as to whether you are in the faith. Test yourselves. Do you not know yourselves, that Jesus Christ is in you?—unless indeed you are disqualified.”
It is too easy to give ourselves the benefit of the doubt.