But is under tutors and governors until the time appointed of the father.
Note 2 at Ga 4:2: The illustration Paul was making is a continuation of his thoughts in Ga 3. In Ga 3:24-26, Paul likened the Law to being our schoolmaster, or "PAIDAGOGOS" (see note 10 at Ga 3:24). There, he was emphasizing the job of the Law (Ga 3:19 and 21).
Here, he was continuing that comparison but emphasizing the effect that relationship had on man. Under the Law, people were no better than slaves. They were constantly being told what to do and actually had no freedom to choose. Through Christ, people have been redeemed from the slave relationship to the Law and are now sons with all the rights, privileges, and freedoms that go with that.