In this chapter of Engaging God's World, Plantinga states that every human has a longing or a yearning for God, it does not matter whether or not the human is Christian or not. It is a desire for something that earthly possessions cannot fill, it is a desire for something more in this life.
This desire can only be filled through Christ. The wicked do not have this desire because God has hardened their hearts so that they do not want him. Plantinga goes on to state that we are made for God. This is true, our only purpose on this earth is to bring honor and glory to the name of God, and to do everything in this life to His glory.