Adoption as Mature Sons and Daughters
In Paul’s time and in Paul's world, babies were rarely adopted. They were simply taken into the home to become part of the family. Adoption was usually reserved for parents who were childless to legally adopt a full grown adult as their son. So really adoption should be called an adult son adoption.
4 But when the fullness of the time came, God sent forth His Son, born of a woman, born under the Law,
5 in order that He might redeem those who were under the Law, that we might receive adult-adoption as sons—(Gal 4:4-5).
What that means for us is that when we become Christians we are placed into the family God not as slaves, nor as over protected children, but as mature daughters and sons of God. That means we don't have to develop our ability to keep a lot of rules. Instead we have to develop an ever deepening relationship to the Father of our family, God the Father. We are adopted into the privilege of adult sons and not slaves or children. We need to develop healthy adult relationships with God the Father.