Jesus took pictures from everyday life to help His hearers understand how God works with people. By using familiar things in life, Jesus enabled a wide range of people to comprehend the truth that He wanted them to learn.
The parable of the laborers in the vineyard teaches that what we receive from God is due solely to His grace. The teachings of the Pharisees was that people could earn God's favor by their righteous deeds. Jesus' story demonstrated that God compensates people according to His own goodness.
When the laborers who had toiled the full day complained that they should receive more than those who had worked for only a short time, the owner answered them. They had received what they were promised. As the owner, he could treat others graciously if he so chose.