I remember living in NYC and seeing day laborers hanging around outside small neighborhood grocery stores. If someone didn’t pick them up early in the day for a job, they would stick around hoping someone would come by later. But you can bet that the ones who got picked up later got paid less than the ones who left earlier!
Not so in our parable. Here Jesus, on the heels of the incident with the rich young man and the ensuing discussion, teaches his disciples that rewards are Gods to give out. They need to be thankful for what they receive, and not jealous of what anyone else gets. If they are serving for rewards they will find themselves last, and others who serve with humble hearts will find themselves first. So we shouldn’t be jealous of what other believers receive in this life or the next. We should trust that God is righteous, generous, and gracious in His dealings with us.