God
(Isa. 40:25; Matt. 28:19; Deut. 6:4)
The Bible is the authority on what we believe, and we can understand it systematically. Greek Philosophy has attempted to make sense of the world using reason, using several branches of thought: Epistemology, the study of knowledge, asks "How do I know?" Metaphysics, the study of existance, asks "What is there?" Ethics, the study of values/morality, asks "What should I do?" Categorical Philosophy asks "Why do I do this?"
The Bible has answered all these questions, and we have learned to study it systematically. Our systematic theology consists of Theology Proper (the study of God), Christology (the study of Jesus), Pneumatology (the study of the Holy Spirit), Bibliology (the study of the Scriptures), Anthropology (the study of Man), Hamartiology (the study of Sin), Soteriology (the study of Salvation), Ecclesiology (the study of the Church), and Eschatology (the study of the End Times).