Jesus is fully aware of our human tendency to mentally lynch each other up from tall oak trees with few, if any questions asked, and he's going to encourage us to establish a kind of “Mental Due Process” before we make judgments about people or situations that we encounter in our lives!
What did Jesus meme when He said "Do Not Judge”? He was saying there’s a much better way to live and that better way is to remember to judge others the way you wish to be judged, judge others with the self-awareness that we tend to be far more critical of others than we are of ourselves and to judge others only after thorough self-evaluation.