Judge not, that you be not judged. 2For with the judgment you pronounce you will be judged, and with the measure you use it will be measured to you.
I used think that this verse should be understood this way: if you judge someone, you will end up committing the same mistakes and therefore be judged in the same way. Don't judge and you will be spared of making the same kind of mistake.
Now I understand it differently. If we make judgments on others, we will be judged exactly as we judged. Not because we will become worse than we were, but because we have always been just as bad as everyone else. As we are no different than those we judge, we will face the same judgment in the end. We are all the same.
The only difference between those who judge and those who refrain is that the latter allows the true judge to do his job. When we refrain from judging and let Jesus do his thing, we become partners in his work of showing mercy. As those who show mercy, we'll be shown mercy by the true and ultimate judge.