In the days of Jesus, the people used to work for twelve hours in a day. They would receive a wage of one denarius for that twelve hour shift,. Jesus tells us, that the Landowner is God the Father. When we are serving God, we can expect to receive something from Him. God Himself tells us, that it is not in vain that we are serving the Lord. He is no respecter of persons and treats all the same. He is an honest employer.