Limitless spending

The word “prodigal” does not mean “wayward” but, according to Merriam-Webster’s Collegiate Dictionary, “recklessly spendthrift.” It means to spend until you have nothing left.

This term is therefore as appropriate for describing the father in the story as his younger son. The father’s welcome to the repentant son was literally reckless, because he refused to “reckon” or count his sin against him or demand repayment.

Source: Prodigal God by Tim Keller

It's a representation of the Good News.

With God, He can spend His forgiveness on us because He always has something left.