While the various theological disciplines are peers, each operating with their own independent and valid methodologies, there is also a kind of normative order to them which is dictated by the one object which they study in common. Because Christianity is based on scriptural revelation, the biblcial disciplines have a decisive priority when engaging the content of the faith. As Scripture is absolutely primary, the disciplines that engage it directly are at the fron of the line: exegesis and biblical theology. As contemporary thinkers undertake the task of interpreting Scripture, historical theology steps next into line, for these texts and concepts have a history of effects in the interval between their time and ours. Christian theology is a long conversation with Scripture, and historical theology attends to the earlier voices in the conversation. Philosophical theology, understood modestly as the discipline that ensures terms are being used clearly, unambiguously, and consistently, is involved all along the way, but it becomes especially prominent after the biblical and historical scholars have given their account of what Scripture says and what the Christian tradition has thought it says. A more robust kind of philosophical theolgy does not just clarify terms but also metaphysical and epistemological commitments that it seeks to coordinate with the revealed truth of Scripture. This kind of philosophical theology shares space (and sometimes disputes turf) with the discipline of systematic theology, whose task is to synthesize exegetical, biblical, and historical theology in order to restate it in contemporary terms. Biblical and historical theologies can limit their projects to careful descriptive work in a historical past tense, but at the level of systematic theology, truth claims must be phrased in the present tense. Last in line, logically speaking, are a host of practical disciplines such as ethics, homiletics, counseling, Christian education, spiritual formation, and apologetics. These fields begin their work in a receptive mode, taking theological truth and applying it to current events, the life of the church, and actual people.
This schematic account of the order of the theological disciplines is a sketch that could probably start a real faculty brawl at most good schools of theology. While it is not quite fair to the boundaries of any of the discipliens, it serves as a good first statement on the chain of command among the disciplines.
Fred Sanders, Jesus in Trinitarian Perspective, p. 10-11