By teaching “Do not judge” (Matthew 7:1), the great teachers are saying that you cannot start seeing or understanding anything if you start with no. You have to start with a Yes of basic acceptance, which means not too quickly labeling, analyzing, or categorizing things as in or out, good or bad, up or down. You have to leave the field open, a field in which God and grace can move. Ego leads with no, whereas soul leads with Yes.
The ego seems to strengthen itself by constriction, by being against things, and it feels loss or fear when it opens. No always comes easier than Yes, and a deep, conscious Yes is the work of freedom and grace. So, the soul lives by expansion instead of constriction. Spiritual teachers want you to live by positive action, open field, and studied understanding, not by resistance, knee-jerk reactions, or defensiveness, and so they always say something like, “Do not judge,” which is merely a control mechanism.
Words and thoughts are invariably dualistic, but pure experience is always non-dualistic. You cannot really experience reality with the judgmental mind because you are dividing the moment before you give yourself to it. The judgmental mind prevents you from being present to the full moment by trying to divide and conquer. Instead, you end up dividing yourself and being conquered.
+Adapted from The Naked Now: Learning to See as the Mystics See, pp. 46-47, 49-50, and When Action Meets Contemplation (Recording).