Unity of all knowledge, language. When I research the meaning of a word, I find myself exploring other words and learning new meanings of words that I already know. It does not take long to realize that all words, that is, language is a unity in which all words are related to all other words and dependent upon this interrelationship of meanings.
The difficulty of philosophy… words and authors and culture. It seems that every philosopher must invent new words and new meanings of extant words. Thus, to really understand an author, one must learn a virtual vocabulary which may be quite large. If one considers the size of a dictionary, e.g., The Oxford Dictionary of the English Language, and multiply that by all the philosophers of history, it becomes impossible to grasp the entirety, and very difficult to grasp any real understanding of anyone. Just consider how many interpreters of every major philosopher of history… how does one know with any certainty just what to original author said. Thus, the “hermeneutical turn” of postmodernism.
Only the Christian can “know.” If one does not know everything, then what one does not know could refute everything that one believes that he knows. Since Scripture was written by an omniscient One, then its knowledge cannot be refuted. “We have the mind of Christ” (I Corinthians 2:16), and “If you continue in my Word… you shall know the truth and the truth shall make you free (John 8:31-32). Only the Christian can truly “know.”