"Just as no particular branch of knowledge is self sufficing so all branches together are not self-sufficing without the queen of knowledge, philosophy." High praise for a discipline that many of us have encountered as confused and obscure rather than deep and clear. The Intellectual has in mind the philosophy adopted by St. Thomas and not the type of vain philosophy most of us studied in college.
We may need to do a lot of unlearning and relearning in our study of philosophy because the "philosophies" of our time have seeped into our way of thinking through our experiences and language.** For instance, we may find it very difficult to conceive of totally immaterial "principles," such as form and matter, which are the backbone of philosophy of nature in the Aristotelian-Thomistic tradition. Most of us have subconsciously inherited the materialistic idea that all things, even ideas, can be reduced to little balls or atoms. This idea is then reinforced by our conscious thought which rarely sees a need for a new paradigm because we rarely need to consider philosophical questions like, "what is change" or "what does it mean to exist."
In determining how to study philosophy and from whom, exercise great caution because there are many good people teaching deceptive philosophy. Also, philosophy forms the foundation of your entire intellectual edifice, so it is worth heading St. Thomas's echo of Aristotle's warning that "a small mistake in the beginning, is a big one in the end."***
Now that the alarm has been sounded loud enough, why is philosophy so important? Simply put, philosophy provides knowledge of the first principles or causes of everything, meaning all the other disciplines. Before we can study what the causes of a particular historical event were, we need to understand what a cause is! In order to relate economic principles to first principles, we need to know what a principle is and what the first principles are! Only in this way can we know our field of specialty from its roots. This helps us avoid serious errors in our specialized study that we will be unconscious of because we don't have the philosophical framework to recognize the error. For instance, many financiers applaud the firing of employees in a healthy company because profits will quickly increase making the company "healthier." The reality of how job cuts affect a company and its current and past employees, however, is much richer than this "profit calculus." This hypothetical financier has, perhaps, given more importance to profit than persons in his "intellectual framework" despite the fact that he understands that people are more important than money in a general way.
Without a grounding in true philosophy, there will be disorder in thought. A problem, which the catholic intellectual must remedy not exacerbate. "If the intellectual Catholic belongs to his time, he can do nothing better than work, for his part, at restoring the order that we lack."
*quotes are from "The Field of Work," section I.
**For a more thorough description of this phenomenon, please see the chapter called "The Greatest Resource -- Education" in E.F. Schumacher's Small is Beautiful.
***De Ente et Essentia