The first rule of understanding the meaning of any passage is to explore its context. Matthew 7, which contains the teaching against “judging,” is the final section of Jesus’ sermon.  Jesus contrasts the expectations of the Pharisees with the true standards of righteousness that He expects from those who are His disciples. Jesus’ does not ignore the Law of Moses, but nor is he contrasting His teaching with the Law of Moses. He is only demonstrating that the heart is the source of love and true devotion and, if present, will fulfill the law. Elsewhere, Paul teaches the same thing. Romans 8:4 reads, “That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit.” Romans 13:8-10 tells us that love is the “fulfilling of the law.” For example, if you love your neighbor, you are not going to covet his wife. This concept is involved when discussing purity and holiness, both of which are focused on a genuine condition of the heart. The Jews, like so many religious people today, are focused on making good appearances. In this case, the greatest motivation is not love for God, and therefore, abstaining from sin and its practice. They are not as focused on what God knows but on what their neighbor or community knows. Consequently, such goals focus on external compliance. For them, as long as we keep up appearances and produce the exact obedience of the law as any other devotee, we are accepted by God. Matthew 6 starts out repeating that their intent is to be “seen of men.” Even after reading such passages, many today never see themselves fitting that description. They may even cry, “Judge not that ye be not judged” while doing the same thing. We see this with “back-seat drivers” and on job sites. When a mistake is made, such people will bring attention to it. It’s an effort to separate you and your errors from them. When they make blunders, which may be as bad if not worse, nothing dare is said to shift the fault and the “beating post” onto them. As long as they can have another outside person that they can cuss out and take out their frustrations, they will feel better. And, for the casual observer and supervisors, they will look better. This is so prevalent in everyday life, that you can hardly miss it. This is the same point that Jesus is addressing when condemning judging. It is when we accentuate the inadequacies and errors in others while ignoring the glaring mistakes in our own life.
The righteousness that Jesus requires is internal and genuine. There’s nothing fake about it. It is true that a pretender can look just the same as the pure in heart, but God knows the heart. By heart, He means the hidden intent and motivation behind the actions that are observable. If human beings are more concerned with what people see from them, then the driving force behind their actions is to make a good showing. Being righteous is not as important as appearing righteous.