What does Galatians 2:18 mean?

Paul has proclaimed that nobody can be justified before God by the works of the Law. Everybody must be justified by faith in Christ or they will not be justified—"made righteous and acceptable" in the eyes of God—at all. Adding any component of works, or some requirement of rituals or deeds, destroys the truth of that good news (Galatians 1:8–9; 2:16). Paul then followed that statement with an objection raised by the critics of this gospel of God's grace. If those who claim to be justified before God through faith in Christ continue to sin, doesn't that make Christ a servant of sin? Paul's response was "Certainly not!"

Christ does not promote sin, and God's forgiveness does not condone sin. To suggest otherwise is a colossal mistake (Romans 6:1; 6:15; Galatians 3:21). Now Paul shows there is much greater danger of increased sinfulness by building a new law than by living freely in God's grace. He says that if he rebuilds (the law) after tearing down (the law), he makes himself to be an even greater sinner. It's law that reveals and promotes our sinfulness, Paul will say, not the free grace of God through faith in Christ.