Why does the human heart long for God?

Religious people would, of course, say that the human heart longs for God because we are God's creations and we instinctively long for our Creator. There are also some other possible explanations. Human existence as we know it includes a great deal of injustice and suffering, and often does not really seem to make sense. We are generally not satisfied with the world we live in, and we want more. The idea that there is a higher level of reality, a supernatural realm, ruled by a wise, powerful, and benevolent deity, who will in the fullness of time correct all injustices, reward the good and punish the bad, and who will grant us eternal life, is very comforting. I cannot prove that any of those things are true, but I would certainly like them to be true.