The Parable of the Prodigal Son is one of the most willfully misunderstood stories in the New Testament. It does not teach that there is no reward for being good. Indeed, the prodigal soon never regains his inheritance. As the father tells the good son, "everything I have is yours".
The moral of the story is that one should forgive. The father forgives the son, and welcomes him back. Indeed, he sees it as a kind of resurrection. What the father does not do is forget. The prodigal son is left to be a workman.
This ties in with the trancendental nature of Christianity. The works of this world are irrelevent to salvation. God does not care about matter. What He does care about is love. At the end of the parable the Prodigal Son is penniless (irrelevent) and loved (invaluable).