If the Galatians begin to keep the 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 the 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 C'est pour la liberté que Christ nous a affranchis. Demeurez donc fermes, et ne vous laissez pas mettre de nouveau sous le joug de la servitude.