Why was the Law given?

Les teaches that the Law was intended to do for Israel what a hired servant or schoolmaster did for a child: prepare, and prepare, and prepare, bringing the child to the place where he could step right in and work with the Father. He explains that the Scriptural word "adoption" did not mean taking a child from another union, but being placed as a full operating son on equal basis with the Father in responsibility and function. Paul uses that term as a schoolmaster. That is what the Law was intended to do for Israel: prepare them so that when the Messiah would come, they were ready. In faith they could have said yes, and a few did, but for the most part the nation rejected it. They could have believed everything Christ was had they been ready, but they were not. Les then applies this to the Gentile economy, saying it is still a valid concept that the Law was given to prepare everything for the coming of the Messiah, that He could fulfill the work of the Cross. He had to die, be buried, and be raised from the dead for our justification. But now the Law has been...