"Judge not, and ye shall not be judged" this statement, and its parallel in Matthew 7:11 is often misconstrued. It means not to act as God in passing some final judgment upon individual, because we can not fully see motives, we often judge falsely. God's people are to be discerning. We must be able to identify wolves in sheep's clothing, in order to warn others and to flee ourselves.  As Jesus suggests in verses 43-44, the fruit one produces is an indication of what he is like.