In the first chapter of Engaging God's Word Cornelius Plantinga Jr. talks about longing and hope. He talks about the sort of things that we long for and what we should long for. In a quote by C.S. Lewis, Lewis talks about how most humans are too short sited; we long for things that will bring us temporary happiness such as alcohol or sex. Those are two pretty extreme examples, but any material items we long for lead us astray. We should not want things.
Jesus told us that the two most important commandments are to love the Lord your God with all your heart and to love your neighbor as yourself. Doing these two things will bring lasting happiness. If we give and show love it will be given back to us.
In desiring the wrong things that only bring temporary happiness we make ourselves into a sinful person. There are two people we can be, the person we want to be and the person God wants us to be. The person we want to be is fallen and sinful. We go after shallow things that will never really make us happy. Most people chose to be this person, but God wants us to long and hope for good things like helping others. The person God wants us to be is ultimately a better and happier person.
We should all long for shalom. Shalom is the Hebrew word for peace. Plantinga says that shalom is basically the way things are supposed to be. God wants us all to live in this peace with him. Shalom can only be grasped by longing for good and pure things.