Are you envious because I am generous? Matthew 20:15b
“The story is as clear as it is unexpected. Whereas we take it for granted that harder work deserves greater payment, this employer operates on a less conventional basis. The reader instinctively sympathizes with the aggrieved workers in vv. 11-12: it doesn’t seem fair. The retort of the landowner is of course technically correct: no one has been cheated; the agreement has be scrupulously observed. Why then do we still feel that there is something wrong? Because we cannot detach ourselves from the ruling convention that rewards should be commensurate to the services rendered…But the kingdom of heaven does not operate on the basis of commercial convention. God rules by grace, not by desert…The God who is generous far beyond what could be expected is never less than just.”
R.T. France in The Gospel of Matthew (NICNT; Grand Rapids: Eerdmans, 2007) 748, 751.