The Fruit of the Spirit is GOODNESS.
Galatians 5:22-23 says, "But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law."
Our God is good. Therefore, goodness is the nature and character of God. It makes perfect sense that one of the Fruits of the Spirit is goodness.
Goodness begins with a love relationship with God. It is through His power that we are able to demonstrate goodness. Why does God want us to demonstrate goodness? Because it is good for us and good for those around us. We are to be a light showing what is truly moral - the beneficial commandments and righteousness of God.
Goodness is acting like Jesus. It is both refusing to do evil and choosing to do things that help others, whether or not they deserve it.
Our goodness should be something that other human beings can be thankful for, just as we are thankful for the amazing goodness God has shown to us.