What is the story in Matthew 20:1-16 about? Why is it told?

This was one of Jesus’ parables: For the kingdom of heaven is like a landowner who went out early in the morning to hire men to work in his vineyard. He agreed to pay them a denarius for the day and sent them into his vineyard. About the third hour he went out and saw others standing in the marketplace doing nothing. He told them, ‘You also go and work in my vineyard, and I will pay you whatever is right.’ So they went. He went out again about the sixth hour and the ninth hour and did the same thing. About the eleventh hour he went out and found still others standing around. He asked them, ‘Why have you been standing here all day long doing nothing?’ ‘Because no one has hired us,’ they answered. He said to them, ‘You also go and work in my vineyard.’ When evening came, the owner of the vineyard said to his foreman, ‘Call the workers and pay them their wages, beginning with the last ones hired and going on to the first.’ The workers who were hired about the eleventh hour came and each received a denarius. So when those came who were hired first, they expected to receive more. But each one of them also received a denarius. When they received it, they began to grumble against the landowner. ‘These men who were hired last worked only one hour,’ they said, ‘and you have made them equal to us who have borne the burden of the work and the heat of the day.’ But he answered one of them, ‘Friend, I am not being unfair to you. Didn’t you agree to work for a denarius? Take your pay and go. I want to give the one who was hired last the same as I gave you. Don’t I have the right to do what I want with my own money? Or are you envious because I am generous?’ So the last will be first, and the first will be last”—Jesus Christ, Matthew 20:1-16.
This is a simple story of grace. God is represented by the character of the landowner. The vineyard represents the activity of the Kingdom of God in this world. The people hired at the beginning of the story represent people who see themselves as having great value to God. The ones progressively throughout the day, right up until the last, are those who are simply desperate to work for the Master. Our “worth” to our landowner is found in a resume of our accomplishments and sacrifices, but rather in simply serving from a heart responding to God’s grace. It’s God that gives us our value. And that’s the bottom line in this story—no one got cheated; everyone was seen as equal in the eyes of the landowner. Since it was his land, his operation, he could do what he wanted. What does that mean? It means that the thief on the cross to whom Jesus promised Paradise that very day he died by crucifixion will enjoy the same blessings of heaven as the person who has worked for the Kingdom his or her entire life. It means that the person who receives Christ in a deathbed conversion will enjoy the same blessings of heaven as the person who has ministered for decades. In that context, heaven will be the same for everybody. As Paul noted in his letter to the church at Rome, What then shall we say? Is God unjust? Not at all! For he says to Moses, “I WILL HAVE MERCY ON WHOM I HAVE MERCY, AND I WILL HAVE COMPASSION ON WHOM I HAVE COMPASSION.” It does not, therefore, depend on man’s desire or effort, but on God’s mercy—Paul, Romans 9:14-16 (quoting Exodus 33:19). If we get into a comparative study of our accomplishments and sacrifices versus everyone else, our eye is not on the Master or His grace, but rather on our own ego. That’s not what the Kingdom is about.