The more “systematic” one’s conception of theology the more one would be inclined to believe that theological propositions exists within a “tight” deductive frame. “Everything is connected to everything else” as Lenin was reported to have remarked. The idea is that changes in one part of theology would have all kinds of “implications” or “ramifications” or “consequences” to other parts. There is a tendency therefore to accept a theological system as a “whole package” seeing each component as entailed by the other.
On the other hand, I tend to think of theology as largely “modular”, that is, theology consists of a lot of loosely connected but detachable components which has very little effect upon each other. On this idea, there are as many possible permutations of theological opinions as there are theological options for each issue. For example, I have a largely Zwinglian opinion on the Lord’s Supper. There is no real presence of Christ’s body and blood in the Lord’s Supper, not even “spiritual” presence or whatever. It is a pure memorial, there is simply no consecration of the bread and wine. Yet I would hold as rigidly to the “manducatio impiorum” as any Lutheran in that I affirm that whoever takes and drinks the bread and wine celebrated in the memorial of the Lord’s Supper, whether he be faithful or faithless, receives the body and blood of Christ. The thing promised, the body and blood, is given to whoever fulfils the terms of the institution (the eating of the bread and drinking of the wine) regardless of their subjective state.
This is one example of a rather unusual combination of theological opinions which tends to resist “systematic” frames. Another very interesting example is how Pelagius affirms very strictly in his commentary on the Romans to justification by faith alone (he uses that exact phrase repeatedly) to the exclusion of works, and even seems to teach a form of the imputation of Christ’s righteousness or active obedience to the believer by a forensic declaration, and yet he is reviled as one of worse heretics in Church History for arrogating human merit and works righteousness, etc, to the exclusion of grace. Certainly he does exalt natural ability in his writings, yet the point is that we have here another interesting theological combination which would drive the systematician mad.
Thus in effect, a lot of what systematic theologians do, that is, drawing out all kinds of “implications” out of individual propositions, are largely in effect a waste of time. Ultimately if we think of the task of theology as that of facilitating the communication of Scripture’s meaning and not inventing new categories and terms for theologians to play with, then systematicity, especially when it abstracts from the particular immediate context of Scriptural passages by general all-encompassing deductive categories, would not be facilitating the communication of Scripture’s meaning but instead be obscuring it instead.