Why do we need the systematic study known as theology? Reformed theologian Charles Hodge explains:
It may naturally be asked, why not take the truths as God has seen fit to reveal them, and thus save ourselves the trouble of showing their relation and harmony?
The answer to this question is, in the first place, that it cannot be done. Such is the constitution of the human mind that it cannot help endeavoring to systematize and reconcile the facts which it admits to be true. In no department of knowledge have men been satisfied with the possession of a mass of undigested facts. And the students of the Bible can as little be expected to be thus satisfied. There is a necessity, therefore, for the construction of systems of theology. Of this the history of the Church affords abundant proof. In all ages and among all denominations, such systems have been produced.
Second, A much higher kind of knowledge is thus obtained, than by the mere accumulation of isolated facts. It is one thing, for example, to know that oceans, continents, islands, mountains, and rivers exist on the face of the earth; and a much higher thing to know the causes which have determined the distribution of land and water on the surface of our globe; the configuration of the earth; the effects of that configuration on climate, on the races of plants and animals, on commerce, civilization, and the destiny of nations. It is by determining these causes that geography has been raised from a collection of facts to a highly important and elevated science. [ . . . ]
Third, We have no choice in this matter. If we would discharge our duty as teachers and defenders of the truth, we must endeavor to bring all the facts of revelation into systematic order and mutual relation. It is only thus that we can satisfactorily exhibit their truth, vindicate them from objections, or bring them to bear in their full force on the minds of men.
Fourth, Such is evidently the will of God. He does not teach men astronomy or chemistry, but He gives them the facts out of which those sciences are constructed. Neither does He teach us systematic theology, but He gives us in the Bible the truths which, properly understood and arranged, constitute the science of theology. As the facts of nature are all related and determined by physical laws, so the facts of the Bible are all related and determined by the nature of God and of his creatures. And as He wills that men should study his works and discover their wonderful organic relation and harmonious combination, so it is his will that we should study his Word, and learn that, like the stars, its truths are not isolated points, but systems, cycles, and epicycles, in unending harmony and grandeur. Besides all this, although the Scriptures do not contain a system of theology as a whole, we have in the Epistles of the New Testament, portions of that system wrought out to our hands. These are our authority and guide.