What was the rite of passage called adoption in Bible times?
In biblical usage, adoption was a rite of passage in which a father formally placed a son as a full operating son, equal with him in responsibility, function, and everything else. It was not taking a child from another union into the family, but granting the son full standing to work alongside the father.
Les explains that this adoption was not like modern adoption, where a child from another union is legally brought into a family. When the father agreed the young man was ready to come in right with him in his business, the young man went through a rite of passage called an adoption. It meant being placed as a full operating son of the Father, on an equal basis with Him in responsibility, function, and everything else. Paul uses this term as a schoolmaster: the hired servant was instructed to bring the child to the place where he could step right in and work with the Father. That is what the Law was intended to do for Israel—prepare them so that when Messiah came they would be ready and could respond in faith. A few did, but the nation for the most part rejected it. The concept carries over into the Gentile economy: the Law was given to prepare everything for the coming of the Messiah, so He could fulfill the work of the Cross, dying, being buried, and being raised for our justification.