Paul told the Colossians, "So let no one judge you in food or in drink, or regarding a festival or a new moon or sabbaths, which are a shadow of things to come, but the substance is of Christ" (Col. 2:16-17). False teachers had come into their midst and had judged them as being less spiritual than themselves because they were not abiding by their false interpretations of the Scriptures and by their man-made rules (v. 22). These judgments were pronounced in an effort to make the Colossians feel like they were lacking in their faith and service. This was done as a means of intimidating them into accepting their errors. Paul told them not to allow anyone to judge them by things which were not of Christ.
There is, however, another side of this "let no one judge you" matter that must be considered. We are not to allow anyone to judge us with regard to the "shadow," but that does not means we cannot be judge according to the things that make up the "substance of Christ." We are told to judge with righteous judgment (John 7:24), which means that we can be subject to such judgments ourselves. If I claim to be a follower of Christ, then everyone has the right to examine my life in light of my Master's teaching and "judge" whether or not I am living up to my claim to be a Christian. If something is amiss in my life, my brethren actually have an obligation to bring this to my attention and encourage me to make the needed changes (Gal. 6:1). If their judgment is correct and I need to make changes in my life, then I should be grateful for their judgment.
Christians are not to allow anyone to judge them by any standard other than the New Testament. However, no Christian is above the righteous judgment of those who are seeing his light shine. Let us learn to appreciate the honest concerns of those who want to help us get to Heaven.