Usually people respond to St. Matthew's parable about the workers in the vineyard by saying, "That just isn't fair. People who work all day long should be paid more than people who work a single hour."
It almost goes without saying!
However, the parable isn't about fair wages. The parable was meant to respond to Peter's question which was asked a few verses before this parable begins. "Then Peter said to him in reply, “We have given up everything and followed you. What will there be for us?” (Matthew 19:27)
As human beings we rarely do anything without considering whether it is in our own best interest. We are naturally inclined to think in such terms. Peter's question is one that we pose for ourselves over and over again. Does it make sense for me to help my neighbor? Should I give this panhandler a break? If I pay the boss a compliment, will it help me in the long run?
Sometimes we apply such thinking to our spiritual lives: "This good deed will earn me a higher place in heaven." That's where the parable comes in. The fact is, and Matthew goes to great lengths to illustrate the point, we cannot earn our way into heaven! Nothing we do will save us from our sins. We cannot save up the credit for good deeds done to offset the debits of our sins. We cannot buy God's love! God loves us freely.
God loves us whether we love him all our lives or whether we love him only an hour. God's love for us is not dependent upon what we do. God's love is a pure and simple gift, unearned and undeserved. God's love is NOT about fairness in our economic landscape.
We don't love God because it will earn us a higher place in heaven. We love God simply because God has always loved us.