The word ‘prodigal’ does not appear in the Greek text. It is an English word that has become attached to the parable of the two lost sons in Luke 15. But it is a good, suggestive word that helps us understand the parable’s teaching.
The word ‘prodigal’ is an English word that means recklessly extravagant, spending to the point of poverty, of ‘being in want’ (Luke 15:14.) The dictionaries tell us that the word can be understood in a more negative or a more positive sense. The more positive meaning is to be lavishly and sacrificially abundant in giving. The more negative sense, is to be wasteful and irresponsible in one’s spending. The negative sense obviously applies to the actions of the younger brother in the Luke 15 parable of the two sons. But is there any sense in which God can be called ‘Prodigal’?
Read the rest of Keller’s response here.