The current controversy over eternal submission of the Son raises the issue of how different branches of theology are interrelated. For instance, critics of eternal submission make historical theology the standard of comparison (e.g. creeds, confessions, tradition).
There are different branches of theology. For purposes of this post, I'll discuss the interrelationship between exegetical theology, historical theology, systematic theology, and philosophical theology.
1. Exegetical theology
Since Christianity is a revealed religion, revealed truths, revealed propositions, lay the foundation. By the same token, exegetical theology is the starting-point. It attempts to ascertain the meaning of primary source material from which Christian theology derives. When successful, exegetical theology enjoys priority or ultimacy. In principle, if there's a conflict between exegetical theology and historical, philosophical, or systematic theology, exegetical theology trumps the others. In practice, it isn't quite that clear-cut.
2. Systematic theology
Some exegetes make a virtue of compartmentalized interpretations. They deliberately isolate their interpretations of a given Bible writer from the Bible in general. If, however, the Bible is inspired, then exegesis should aim for interpretations that are consistent with the overall theology of Scripture. Interpret the part in relation to the whole.
Systematic theology considers the implicit as well as explicit teaching of Scripture. The logical implications of Biblical propositions, both individually and in their relation to other propositions. And with harmonizing the various propositions of Scripture. To some degree, that's something an exegete must consider on a smaller scale when expounding the "theology of Paul", the "theology of John", the "theology of Hebrews", and so on.
3. Historical theology
Ideally, historical theology codifies received interpretations of Scripture that are true interpretations of Scripture. After exegetical theology has done its job, historical theology codifies the conclusions.
There are situations in which creeds and confessions can be treated as settled doctrine. But from a Protestant perspective, that can't be absolute. For one thing, you have a diversity of theological traditions. They can't all be right. So sifting is necessary.
Even if a creedal statement is true, there are still situations in which it's necessary to scrutinize the claim. Although the Christian faith is true, the Christian faith is new to each new generation. Whether you grew up in the church or were unchurched, it is necessary for you to ascertain the truth of Christianity. So at that stage of the process you are treating these truth-claims as open questions. Even if a theological tradition got it right, assent should be more than an accident of birth or coin flip. Creeds and confessions must be intellectually defensible.
That doesn't mean every generation must start from scratch. Theological traditions represent large-scale interpretations of Scripture. That gives the younger generation some preexisting options to consider. We don't have to reinvent the questions and answers. It is, however, still incumbent on us to assess the received answers.
Moreover, tradition may condition us to only ask traditional questions. But sometimes we need to reexamine old issues from a fresh perspective. Otherwise, we may be stuck in a theological rut. The way an issue is framed can prejudge the answers and artificially exclude a larger range of potential answers. But sometimes we need to think outside the box rather than filtering the discussion through a venerable paradigm.
4. Philosophical theology
There's more to Christian theology than just quoting Scripture. It is necessary to understand what Scripture means. The ability to explain Scriptural propositions in your own words. Define terms. The ability to expound and summarize revealed concepts. Philosophical theology can help to articulate the meaning of Scripture by providing vocabulary and categories.
Exegetes sometimes commit logical fallacies because they lack philosophical training. Exegetes sometimes overlook alternative explanations because they lack conceptual resources. In that respect, philosophical theology can supplement exegetical theology.
Then there's the whole issue of hermeneutics. What is the task of the exegete?
Where is the locus of meaning? Original intent? Should an exegete focus on the original audience or the history of reception? What is the intended audience? Is that the original audience? Or is that the community of faith? Then there's the sense/reference distinction.
These are philosophical questions. In that respect, philosophical theology can supplement exegetical theology.
Philosophical theology can also play a role in defending divine revelation. Likewise, philosophical theology supplies historical and systematic theology with models and metaphors. Traditionally, historical theology borrows distinctions and categories from Platonic and Aristotelian philosophy. But there's no reason that can't be updated by recourse to more recent philosophical developments.