Is biblical adoption the same as modern adoption?
No. In Scripture, adoption meant a rite of passage placing a son as a full operating son of the father, on equal basis with him in responsibility, function, and everything else. It was not modern adoption, which takes a child from another union and legally brings them into a family.
Les teaches that the biblical word adoption is not like modern adoption, which takes a kid from some other union and legally brings them into this one. In the Scripture, a father would agree that the young man was ready to come into his business; after a rite of passage called adoption, he was placed as a full operating son, equal with the Father in responsibility, function, and everything else. Les explains that this is the term Paul uses as a schoolmaster. The hired servant was instructed to bring the child to the place where he could step in and work with the Father. The Law was intended to do that for Israel: to prepare them so that when Messiah came they were ready. A few believed, but the nation largely rejected it. Les says the concept remains valid for 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.