Those who think God is fair may dislike this passage. While he is fair to those who came first, giving them what he promised, he is seemingly unfair to those who came last by giving them the same amount, a day's wages.
God provides what we need. What makes life so miserable is comparing to others, what they have or don't have. Those who had come first would have been perfectly fine if those who came last were given less. What made them really angry was making them equal to those who did the right things and worked so hard.
God blesses those who simply show up, who live in the grace given freely to all. Hell is when we go to heaven and complain about the people who we think shouldn't be there.
Application: Lord, you are merciful beyond our imagination. Help us to simply enjoy it and not compare and complain.
One Word: God is generous.