The church has always had a struggle with legalism right from the beginning and the problem has not gone away. The modern church is still dealing with legalism. To understand the relationship between law and grace, we must clarify the nature of legalism, and what it is not. Legalistic Gospel
Legalism is not dependence on law. Law is good. Every society needs laws to function. Paul had strong words about the value of law.
The law is holy, and the commandment is holy, righteous and good (Rom 7:12).This is clear. Attacking the law will not rid the church of legalism.
The law is spiritual (Rom 7:14).
Abundance of rules is not legalism. Rules can be good. A rule about driving on the right side of the road is useful. However, a massive number of complicated and incomprehensible rules create confusion. Large numbers of detailed rules can be a symptom of legalism, but they is not the cause.
Legalism works at two levels.
The gospel is corrupted by legalism when it is turned into Jesus plus something else that a Christian must do. Legalistic people minimise the gospel, because they assume some other thing has to be done in addition to what Jesus is done. Salvation is partly earned by human effort. In his letter to the Galatians, Paul was dealing with circumcision. Some Christians were implying that faith in Jesus was not enough, so those with faith in Jesus must be circumcised to be fully saved. This gospel was Jesus plus circumcision.
The addition to the gospel can be something good. Other people in Galatians said that keeping the sabbath was essential for salvation. Their gospel was Jesus plus the sabbath. The sabbath is a good thing commanded by the law. The problem is that when a good command is turned into a criterion for saved, very detailed rules are needed, as there is always one more exception that needs to be clarified.
For example, if sabbath is a gift for life given for our blessing and refreshment, “have a good day off” is enough. However, if sabbath is a criterion for assessing who is in or out, precise rules about multiple categories of work are needed. The Pharisees were playing this game. Their detailed rules are the symptom of their legalistic approach to salvation, which required people to earn their salvation by obeying all the rules.
Legalism can cripple the Christian life. Humans seem to have a natural propensity for living by rules. Some personalities are particular prone to this tendency. Christians living can slip into living by a set of rules. A good Christian is the one who does not do things on the forbidden list. This legalistic approach to life fosters pride and exclusivism and leaves many Christians stuck in immaturity and boredom.
Rules are fine for beginners, but as a Christian grows their relationship with Jesus, rules should become less important. The Christian life is following the voice of the Spirit wherever he leads, letting the life of Christ transform our lives. Many ambiguities and tensions will be faced, but these are best dealt with by grace and faith, rather than increasing rules. Walking in the Spirit is much harder and more exciting than living by a bunch of rules.