A good overview of this complex religious phenomenon is available in a recent collection of essays by Jan Assmann, “Personal Piety and the Theology of Will,” in The Mind of Egypt: History and Meaning in the Time of the Pharaohs (New York: Metropolitan Books: 2002), pp. 229–246. Strikingly enough, this phenomenon was also widespread in other parts of the contemporary ancient Near East. See Thorkild Jacobson, “Second Millennium Metaphors: The Gods as Parents,” in The Treasures of Darkness: A History of Mesopotamian Religion (New Haven and London: Yale Univ. Press, 1976), pp. 145–164.