The word religion has fallen on hard times in recent years. Many have tried to pit religion against faith, saying that Christianity isn't a religion but a relationship. That sounds nice, but that isn't quite the case. Faith and religion are not mutually exclusive, they are complementary. Christianity is a religion founded on a relationship with Jesus Christ. In fact, Christianity is the only true religion in the world because it is the religion established by the one and only true God. The Christian religion is the all-encompassing life of trusting, worshiping, following, and loving God and loving our neighbor, enabled by the regenerating and empowering work of the Holy Spirit, and established on our relationship with Christ through the gospel by grace alone through faith alone.
Nevertheless, we rightly speak critically of religion when we speak of man-made religion. When we speak of such religion, we are either speaking of all the false religions of the world, such as Islam and Buddhism, or we are speaking of the religious rules that men add to Scripture and with which they attempt to bind our consciences. This latter type of religion was the religion of the Pharisees and later of the Judaizers. However, the fundamental problem of the Pharisees and Judaizers was not that they were overly zealous about religious orthodoxy, but that they invented their own religious orthodoxy. Based on their man-made legalistic inventions, they judged hearts and tyrannized those whom Christ had set free. And that is the precise problem with all forms of legalism in our churches today. We invent laws around God's law. We attempt to turn our preferences into God's principles. We say "you can't" when God says "you can."
At the same time, we must also understand what legalism is not. Legalism is not obedience to God and His law. Legalism is not learning to obey all that Christ has commanded us. Legalism is not pursuing holiness. Legalism is not striving to please God and glorify God in all that we do. Legalism is not being zealous in our good works and in bearing fruit in keeping with repentance.
Legalism is not an error of Christianity—it's a different religion altogether. Legalism draws attention to us, but gospel religion draws attention to Jesus Christ. Legalism gives us glory, but gospel religion gives God glory. Legalism is rooted in self-worship, but gospel religion is rooted in the worship of God. And the ironic thing about legalism is that it doesn't make people want to work harder, it makes them want to give up.