Is the standard 'pig pen' sermon on the prodigal son good theology?
No. The familiar pig pen sermon makes good preaching, but it is not good theology. The parable's younger son was already a child of God, whereas sinners are born in sin and are not children of God. Applying the pig pen return to a believer's experience does not fit the text.
Les explains that the familiar pig pen sermon on the prodigal son makes good preaching, but it is not good theology. He asks whether the prodigal's state matches our own experience—whether we were once a child of God and then turned away. He says we have always been sinners, born in sin, and all have sinned and come short. We were not children of God, but in the parable both sons were children. That is why the standard application does not fit. The younger son took his inheritance, wasted it in riotous living, ended up feeding swine, and was destitute.