There's some pretty great theology in this passage, and actually pretty simple. Maybe a good way to sum it up might be, "If the best the law had to offer us was a way to to correct the path of Adam, then the best Jesus has to offer us is the news that it's not longer about the path, it's about him." Being slaves to sin was something God always meant to free us from, and the law was the first step, but never the final one. When the time was right, God enacted the upgrade: the Word made flesh, the life of the Spirit.