"See to it that no one takes you captive by philosophy and empty deceit, according to human tradition, according to the elemental spirits[a] of the world, and not according to Christ"(Col. 2:8)
Likewise, Paul refers to Christ as the one "in whom are hidden all the treasures of wisdom and knowledge. 4 I say this in order that no one may delude you with plausible arguments"(Col. 2:3-4).
What implications does this have for us? We oftentimes come across professing Christians who nonetheless differ markedly in certain important doctrines. Sometimes such people argue against our own Calvinistic doctrines according to abstract reason rather than Scripture. Sometimes they do use Scripture, of course. But we must keep in mind that the only legitimate argument for or against anything is appeal to Scripture. For example, an Arminian may argue that Calvinism contradicts the aseity of God because if God's foreknowledge of the salvation of the elect makes it certain, definite and unalterable, this means that God is obligated to save us. He cannot not save us. Therefore, God is dependent upon us for His attribute of aseity. Likewise, a Calvinist may argue the exact same thing against an Arminian, namely, that God's aseity is compromised by Arminians because God is dependent upon an antecedent consideration of His foreknowledge of our decision for Christ before He makes His decision to elect.
Note how abstract, autonomous reason can always go either way. Kant ably demonstrated that one can prove anything (and therefore nothing) with the use of 'pure' reason that is not tested against empirical phenomena. Of course, rather than testing our reason against empirical phenomena, we subordinate it to Scripture. Scripture determines the chain of reasoning and its logical entailment. No one ought to pretend that they are able to infallibly demonstrate that a certain theological conclusion entails by logical necessity. We ought to instead simply determine what Scripture says on the matter. For Vollenhoven, unscriptural reasoning leads to 'synthetic' reasoning. It is synthetic insofar as it synthesizes a non-scriptural and historically contingent mode of thought with Christianity and thereby corrupts it and causes the synthesizer to potentially come to theological conclusions and positions which he might not have had he stuck with Scripture.
This can be a particularly dangerous path to take because there is no telling to where it might lead. Numerous examples of such errors abound in the history of the Church. We must always be on the watch for human philosophies creeping into our theology. The early church writers internalized a great deal of Neoplatonist thought in an attempt to fight the pagans with their own language and philosophy. This is understandable, because much Christian theology is formally very similar. But there are also crucial differences between the two thought patterns. More importantly, there is much in Neoplatonist thought that does not necessarily clearly contradict Christian theology, but nonetheless introduced doctrines into Christian theology which is foreign to it. I would use the example of the eternal generation of the Logos. I believe this is a distinctly Neoplatonistic doctrine introduced by Alexandrian writers like Philo and Origen. Is this doctrine hostile to Christianity? I don't think I would go that far. But I certainly do not believe it is biblical.