Paul wrote the letter to the Galatian churches to oppose those who taught that obedience to Mosaic law was necessary for salvation rather than faith alone. He defended his apostleship and argued that Abraham was justified by faith, not works. Paul explained that the purpose of the law was to act as a guardian until Christ, and that Christians are made perfect through faith in Christ, not by keeping the law. He urged the Galatians to stand firm in their liberty through Christ and to produce the fruit of the Spirit rather than the works of the flesh.