The parables in the Gospels are earthly stories with heavenly meanings. The parable of the workers in the vineyard gives us a glimpse of the upside-down nature of God's kingdom. The first will be last, and the last will be first. Understanding this without a personal revelation of God's disruptive and disproportionate grace is impossible. We cannot earn anything in His kingdom through our human efforts. At first, God's disproportionate grace seems unfair, but would you deny the thief on the cross his salvation because he didn't have a chance to prove his commitment and works?