With these words, Paul is reminding the Galatians that those who seek to earn God’s favour through obedience to the old covenant law will not receive the promised inheritance. The son of the slave will not share in the inheritance with the son of promise. He is not encouraging them to expel the Judaizers, though that would be a natural application to draw from these words.1
30 Mais que dit l'Ecriture? Chasse l'esclave et son fils, car le fils de l'esclave n'héritera pas avec le fils de la femme libre.