Systematic theology covers the major topics of Christian doctrine.  Usually, the topics addressed are revelation, God, the persons of the trinity, humanity, sin, salvation, the church, and last things. An introduction will provide an overview of the Biblical passages relevant to the discussion, some key formulations of the doctrine in church history, philosophical or scientific issues related to the doctrine, and the implications for Christians. Church history examines the expansion of Christian communities. Historical theology covers the development of these topics by Christian leaders.