This is a tough parable to read. In the flesh, I think we have all experienced a little unfairness regarding our own salaries. Certainly, we work hard, but there is always someone who works less and yet they earn more. I don't understand it in the secular sense.
But with Ministry, I think this parable has real value, and should be taught in seminary and in church as a reference to the value of what happens when we proclaim the Gospel of Jesus Christ.
The value of the pastor's work is no more valuable than the janitor's work. The value of the street preacher is no more valuable than the secretary's work. All who proclaim the Mysteries of God and all who labor to lift up Jesus Christ need to remember that the work we do isn't about us. The work of spreading the Gospel, if it were reckoned on the scale of the recordings in the New Testament, would most likely lead to our own crucifixion. We need to stop placing ministers on pedestals, and start working side by side with them to support the advancement of the Kingdom of God.
We will receive the same inheritance, if our name is written in the Lamb's Book of Life. Therefore, put off the childish bickering of what ministerial role is more important.
You are just as valuable, and you will receive the same reward for proclaiming the Gospel of Jesus Christ. So be empowered, and be bold! Lift up the Name of Jesus!