Adoption was a Roman Law. The father in Roman Law had absolute power over his children as long as they lived, even over their life and death. Children never possessed anything. All possessions were the property of the father. To be adopted was to take a serious step. The ceremony included trading the person to be adopted two times between the two parties and taking the adopted person back two times. On the third time the trade was completed.
At that point, the person adopted had all the rights and privileges of the new family and lost all the rights and privileges of the old family. This included all the debts, connection with the previous family, etc. The old family was abolished as if it had never existed. This position came by grace not by right. The adopted son was heir just the same as the natural son. Adoption occurred because of the love of a parent for a child, love which brought him into the family as a full-fledged member with all rights and privileges.
Sonship implied responsibility, also. It is inconceivable that we should enjoy a relationship with God as his child without accepting the obligation to imitate the Father and cultivate the family likeness.
© 1997 Dr. Winn Griffin. New Testament Survey. 46.