Would You Please Explain Legalism?
The word legalism is derived from the concept of legality or law. Paul chided the Galatian church for trying to have a relationship with God based on or including legalities from the Mosaic Law. By obeying these 600-plus legalities, Israel had a contractual relationship with God. We could say, then, it was a laws-driven or "legalistic" relationship with Him.
Two words capture well the Old Covenant Law: excessive and fixative. The 600-plus religious and behavioral laws were, to put it mildly, excessive. And because of the sheer volume and detailed stipulations of those laws, the people had to fixate on them so as to not violate them.
In the New Covenant, thank you Jesus!, we are not bound to a legality-filled contract with God (the Mosaic system). Yet, strangely, the Galatian church was trying to have a relationship with God with elements or portions of that system. They regressed to a laws-driven or legalistic relationship with Him. If you read Galatians slowly and thoughtfully, you will see our two descriptive words: excessive and fixative. The Galatians regressed to an "excessive laws" spirituality, and therefore, a bizarre fixation on keeping them. It became a cancer to their New Covenant intimacy with the Lord.
Legalism Today
In that same spirit or mentality, Christians today sometimes add excess laws or rules to the Christian life that do not appear in Scripture, or, appear ambiguously, or, appear differently in different contexts, or, are drawn from the Old Covenant. They develop a bizarre fixation on these laws or rules, push them on others, and judge everyone's spirituality based solely on them. The most obvious large-scale example would be an entire denomination obsessed with keeping the Saturday Sabbath, when Paul explicitly addressed this legalistic issue with the Romans and Colossians (Ro 14:5, Col 2:16,17). On a smaller scale, Christians come up with all kinds of sanctimonious little religious rules--rules that are not specifically articulated in the New Testament--they think make them more holy and spiritual. It does not. Even worse, God says legalism is a "yoke of slavery...alienated from Christ...fallen away from grace" (Gal 5:1,4).
To keep this at mini-teaching length I will stop there. I have written an extensive article on legalism entitled, The Claws of Legalism. You can read it at the Articles Catalog at the Daily Christian Life Catalog.