In Christianity, legalism is the excessive and improper use of the law (10 commandments, holiness laws, etc). This legalism can take different forms. The first is where a person attempts to keep the Law in order to attain salvation. The second is where a person keeps the law in order to maintain his salvation. The third is when a Christian judges other Christians for not keeping certain codes of conduct that he thinks need to be observed. Let’s examine each one more closely.
The first kind of legalism is where the law of God is kept in order to attain salvation. This is a heresy, a completely false doctrine. We are not able to attain salvation by our keeping the law. Rom. 3:28, "For we maintain that a man is justified by faith apart from works of the Law. Rom. 4:5, "But to the one who does not work, but believes in Him who justifies the ungodly, his faith is reckoned as righteousness.” Gal. 2:21, “I do not nullify the grace of God; for if righteousness comes through the Law, then Christ died needlessly.” It is simply not possible to keep the Law enough to be saved. Therefore, to try and gain salvation through one’s efforts is a false teaching. It is so bad that those who hold to it cannot be Christians since it would deny salvation by grace through faith.
The second kind of legalism is where a person tries to keep or maintain his salvation by keeping the law. This is also a false doctrine. We receive our salvation by faith (Eph. 2:8-9), not by our ability to be good because no one does good (Rom. 3:10-12). As Rom. 3:28, 4:5, and Gal. 2:21 clearly show, we are justified by faith, not by faith and works. Furthermore, there are strict warnings about attempting to keep the law in order to maintain salvation: Gal. 3:10, “For as many as are of the works of the Law are under a curse; for it is written, “Cursed is everyone who does not abide by all things written in the book of the law, to perform them.” And James 2:10, “For whoever keeps the whole law and yet stumbles in one point, he has become guilty of all.” So, if a person is seeking to be either saved by his works (Law) or maintain his salvation by his works (Law), then he is under obligation to keep all of it, and if he does not then he is guilty before God. Furthermore, consider Jesus’ words in Matt. 7:22-23, “Many will say to Me on that day, ‘Lord, Lord, did we not prophesy in Your name, and in Your name cast out demons, and in Your name perform many miracles?’ 23 “And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness.’” Jesus condemns them because they were appealing to their salvation based on their faith and doing good. So it should be obvious that we do not keep our salvation by our efforts.
The last kind of legalism, where a Christian keeps certain laws and regards other Christians who do not keep his level of holiness with contempt, is a frequent problem in the church. Now, we want to make it clear that all Christians are to abstain from fornication, adultery, pornography, lying, stealing, etc. Christians do have a right to judge the spirituality of other Christians in these areas where the Bible clearly speaks. But, in the debatable areas we need to be more careful, and this is where legalism is more difficult to define. Rom. 14:1-12 says that we are not to judge our brothers on debatable issues. One person may eat certain kinds of foods where another would not. One person might worship on a particular day where another might not. We are told to let each person be convinced in his own mind (Rom. 14:5). As long as our freedom does not violate the Scriptures, then everything should be okay.