The following comment was offered as a challenge to my understanding of legalism. Please understand, I don't claim to be a theologian. I have a wide range of readers, and I want to keep what is presented here as accessible as possible. My intention is to avoid subtle technicalities and deal with realities, to the best of my understanding, that everyone can relate to.
When I quote a comment in a new post, I am leaving off names. It isn't because I'm not giving credit--you can look at the comment box and see the names--I just want to separate individuals from concepts and look at the concepts without prejudice for or against, on account of source. I wish I were anonymous. :)
Religious legalism = drawing a definite line where God draws none [often done out of good intent, but with necessarily deadly results, spiritually speaking]. It is taking the spirit of the law and defining it in human terms that can be codified and measured. It is trusting in a human standard to protect righteousness; which then, by default, eventually defines that righteousness.
In practical terms of CHM, legalism is "knowing" who is "worldly" and who is not just by looking at their outward appearance. Or looking at someone's adherence or non-adherence to actionable standards [e.g. ring-wearing or not] and then declaring them as worthy or non-worthy.
Religious legalism is adopting a standard for personal and family life which can be measured in externals -- a standard which CANNOT be definitely termed biblical, but appeals to tradition and sub-cultural mores; and, since it cannot be definitely defined as biblical, it uses inculcated sense and unspoken group pressure to maintain its existence.
Legalism is a [hypothetical] mother who has two daughters who both passionately love the Lord, but she is grieved and heart-broken, often moved to tears because one of the daughters, in following Truth, decides that she is called to wear a wedding ring, cut and style her hair, and wear a sleeveless dress, etc.
Legalism cannot appeal to Scripture alone as its final authority of faith and practice. It always must add a sub-cultural and/or traditional lens as the final arbiter of what is right or wrong, or "desirable."