It is very important to tell the difference between “Systematic Theology” and “Biblical Theology”. “Biblical” theology has the same format as the Bible: “Systematic” does not.
A “Biblical” theology of Jesus might be “Jesus according to Matthew” or “Jesus according to Paul’s letters”. Matthew’s personality is in the choice of words throughout his story of Jesus life. The first four books in the New Testament are stories about Jesus’ life told by different people; they are called “Gospels”. They all tell the truth, but with different personality. The Gospel of Luke is somewhat like an investigative journal while the Gospel of John is more of an empty stage theatrical playwrite. Even when one Gospel quotes Jesus, the words may be slightly different from another Gospel retelling the same story. “Exact quotes” were unheard of at that time, so they accurately include the “voice of Jesus” rather than the “words of Jesus”; though different, they do not disagree. This type of difference is what we find in a “Biblical study of Jesus in Matthew” vs a “Biblical study of Jesus in John”. We can do “Biblical” studies on many things.
When we study a topic from many books of the Bible and compare them so as to paint a more complete portrait, this is called “Systematic” Bible study. You could also call it “Topical”. “Biblical Theology” studies Bible teaching by book; “Systematic Theology” studies Bible teaching by topic, using many books at the same time. It is very important to develop Biblical theology first, then Systematic theology later.
Once we develop a Systematic theology from the Bible, we have what is called a “Doctrine” or a “Teaching”. The best example is the “Trinity”. The word “Trinity” is not “Biblical”, but theologians use that word to describe the Systematic theology that God is Father, Son, and Spirit. So, the “Doctrine of the Trinity” could also be called a “Systematic Theology of the Trinity”.
If a Doctrine is against the Bible’s teaching, however, this is called “Unbiblical”.
In 1989, John MacArthur published the book “The Gospel According to Jesus”; in 1991 Don Carson published “The Gospel According to John”. One was Systematic, the other Biblical. Know the difference.
Proverbs 16:25, Matthew 28:19, John 16:12-15; 17:20-23