The parable of the prodigal son as incomplete gospel

The parable of the prodigal son is receiving a lot of attention at the moment. So I thought I'd share a taster of PT Forsyth on the passage:

There are those who say you have the whole of the gospel really in the parable of the prodigal son, that that was the culmination of Christ's grand revelation of God...But you have not the whole gospel in the parable of the prodigal son...

Now the one ruling idea in the parable of the prodigal son is the idea of the centrality, the completeness, the unreservedness, the freeness, fullness, whole-heartedness of God's grace - the absolute fullness of it, rather that the method of its action. But however a parable might preach that fullness, it took the Cross and all its train to give it effect, to put it into action, life, and history, to charge it with the Spirit...Hence as to the method of God's free and flowing grace the parable has nothing to say. It does not even say that the father was seeking the prodigal. The seeking grace of God we find there as little as the redeeming grace....

[The prodigal can only be sure of the father's forgiveness if] the father not only says but pays. His mere repentance could not make him sure, could not place him at home again, could not put him where he set out. His mere repentance could turn his heart to his father, but it could not break the bar and fill him with certainty of his father's love and forgiveness. And that is what the sinner wants, and what the great and classic penitents find it so hard to believe. Now, the parable tells us of the freeness of God's grace, and its fullness, but the Cross enacts it and inserts it in real history. It shows to what length that grace could go in dealing with a difficulty otherwise insuperable when we turn from a single prodigal to a world...the act of Christ's Cross - is not simply to produce individual repentance, but it has its great effect upon the relation of the whole world to God. And the judgment, the payment, was on that scale. (The Work of Christ, pp.106-111)