The way up is the way down. A. Parable, like many others, has two aspects to it. God is generous and good. Second - many people cannot accept God's goodness. B. Parable addressed to Pharisees, who rejected Jesus.
Selfishness is one of most common human traits.
We tend to identify with first workers, like the Pharisees did. It violates our sense of justice. We are too quick to judge salvation of others. But if we want salvation by grace for ourselves, we shouldn't begrudge it to others. Too many are filled with resentment toward others.