In 2nd Timothy 3:16, the Apostle Paul refers to the Scriptures as 'God-Breathed'. It is the very Word of God and as such it reveals a great many truths about the way the world is, why it is this way, the true nature of reality, as well as what is to come. It explains how and why the world is broken and how mankind can be reconciled to God through the Person of Jesus Christ.
These are all doctrines or teachings and yet due to their complexity there has always been a drive to take the various concepts and form them into a system-oriented theology. But how is this to be done? Historically theologians have resorted to philosophy and its ideas and categories regarding things like the nature of knowledge, how truths relate to one another in terms of coherence - think of a grid in which the various lines and points interrelate and connect to one another. Using this methodology, theologians are able to sometimes 'fill in the blanks' where the Scriptures don't always spell things out clearly. They can use deduction and sometimes even speculation. Often standing on the shoulders of thinkers like Aristotle and Plato, the philosophical toolbox of these theologians grants them no small degree of confidence in their intellectual exercises. In terms of Church History, this tendency reached its peak during the High Middle Ages with thinkers like Thomas Aquinas (d.1274) and Duns Scotus (d.1308) and again in the 17th century when this 'Scholastic' tendency appeared among Protestants as they drafted their Confessions.
Systematic Theology is wide ranging and the various books that are produced are often impressive - over 1000 pages is not uncommon. Such works are dense, detailed, highly penetrating, and yet there are some that have become critical of this method and would argue there's another and better way.
First, it should be noted that God did not reveal His doctrines by this means. The Scriptures contain no systematic expositions or encyclopedic approach, but rather Divine Truth is revealed through histories, wisdom literature, poetry, prophecy, and epistles. These writings were produced within specific contexts that are very important to properly understanding them. There are repeated themes, symbols, foreshadowing - so much so, that some unbelieving scholars simply argue it is a production and no real chronicle of God's work among His people.
It can be argued that a systematic approach cannot properly differentiate between the Old and New Testaments and often must create categories (that sometimes have no real Biblical warrant) in order to force things into a logical order. The New Testament often interprets and offers a divinely inspired commentary on the Old Testament and frankly, the apostolic writers don't seem to interact with the Old Covenant writings the way the theologians do - a fact both sobering at comforting.
The New Testament reveals that the entire Old Testament order anticipated the New Covenant. In fact Christ is revealed as being the central focus of the entirety of Scripture - it's organizing principle as it were. As the logos (John 1:1), he is the Word that is central to all Divine knowledge. Sadly, some have reduced this logos concept to mere human logic - equating Christ and God with logic and reason. In actuality John is revealing that regenerate reason rests on faith in the mystery of Christ-centered knowledge (or epistemology) - a point echoed and elaborated by Paul (Romans 16:25, Ephesians 3:4-9, Colossians 1:27, 2:2, and 4:3).
Paul declares that all the promises in Him are 'yea' and 'amen' - that is affirmed and confirmed (2nd Corinthians 1:20). There are no promises fulfilled outside of Christ. It must be said this basic Christocentric key to understanding Scripture is actually rejected by many of the dominant theologies of our day. Some even insist that certain promises have to be fulfilled apart from Christ. Others make certain philosophical commitments (such as to man's freedom or moral capacity), while others make doctrinal commitments such as a belief in a Christian world order or that God has separate plans for the Jews and the Church. All of these commitments shift attention from the central focus of Scripture which is Christ Jesus.
To be continued....