The history of adoption and the biblical references become illuminated with this information so give it a read if the subject interests you. The legal situation of a son in Roman times was little better than a slave. The adopted son was equal to one born in the family. We were not merely children who needed to grow up, but rather slaves of sin who needed redemption. We needed to be bought out of bondage to a new family that Christ brought into being by His death and resurrection.
Adoption expresses redemption and new relations of trust and love.
It is shown spiritually from slavery to sonship and heirship. Adoption is more than a matter of position or status. He puts His spirit within us. He becomes Lord of our lives. We cannot imagine the things He has prepared for those who love Him.