If the Galatians begin to keep old covenant law as a means of justification, they are returning to a system of slavery, walking in the ways of Hagar and Ishmael (Galatians 4:24–25) rather than Sarah and Isaac (Galatians 4:26–28). Instead of doing this, they must continue to live free from the demands of old covenant law (Galatians 2:4), confident of justification in God’s sight through faith in Christ (Galatians 3:13; Galatians 4:5).1
1 For freedom Christ has set us free; stand firm therefore, and do not submit again to a yoke of slavery.