There are two dimensions or aspects of theology that you have to acknowledge when attempting to define it, both with their own distinct character—the academic and the spiritual. The academic aspect of theology was defined by 20th century theologian, Aiden Nichols, as being "a disciplined exploration of divine revelation." St. Anselm, an 11th century theologian, defined the spiritual aspect much more simply as "faith seeking understanding." Before we go into what these mean, it’s important not to think of these as two alternatives or options of how to look at the matter, nor even two sides of the same coin. But, rather, they are two poles between which in a tension sits theology proper, which is a balance between faith and reason. If we deny the academic, as is often tempting to do, and rely only on the spiritual, then we deny the necessity of reason, thereby allowing anything prayerful or contemplative to be considered theology. If we rely only on the academic and deny the spiritual aspect, then we eliminate the need for any active faith or belief in what we study, thereby reducing theology to some kind of clinical process or case study.
The academic definition, again lending itself more to a conventional scientific approach, highlights the nature of theology as a science in its usage of terms and bears dissecting: “A disciplined exploration of divine revelation.” By “divine revelation” we mean Sacred Scripture and Sacred Tradition (notice the use of uppercase letters, which indicates the formal scriptures and traditions of the specific religion in question, in this case Christianity)—the Bible and the Church traditions passed down by apostolic succession. “Exploration,” being the bridge and balance between two elements of “divine revelation” (aligned with faith) and “discipline” (aligned with reason), is the elevation of the mind through philosophy to understand divinity, which is the ultimate goal of theology. “Discipline” characterizes the approach to spiritual topics as being well-ordered and coming from man’s natural gift of rationality, namely that it’s philosophical. It then stands to reason that theology is itself a science and that it generally follows (though not in every way) basic scientific guidelines.
Theology seeks to understand the Creator through creations.
The Greek philosopher, Aristotle, defined science as “a deductive system of thought that aims to explain affairs we observe by tracing them with necessity to principles that provide a causal account of them.” That’s kind of a mouthful, but it really just means that we carefully look at one thing and try to explain how it happened by going back to its various causes. With that in mind, the International Theological Commission in turn defined theology as “a scientific reflection on divine revelation which the Church accepts by faith.” So, the articles of faith (Scripture, Tradition, etc.) are the principles of theology (just like gravity and motion are all accepted principles of the science of engineering), and the highest of these principles is divinity. The empirical sciences (e.g., biology, geology, etc.) all proceed from the assertions of higher sciences (again, as does engineering from physics). So, theology seeks to understand divinity by tracing creation backwards, in essence to understand the creator through creations, since the material world and history constitute the space and time in which God reveals Himself to us. Since science and reason are the highest forms that a rational mind can attain, and the object of theology is the highest form that exists (i.e., divinity), then theology is not only considered a type of science, but it’s actually the highest type of science.
Since the Church (as in the whole body of religious believers) accepts the principles of theology by faith, then faith must play a vital role in theological study (again, reason and faith). As other sciences rely on the principles of a higher science, then one has to invest some belief in the higher principles to understand the effects that result from them (e.g., you can’t study biology if you don’t believe the principles of chemistry). Therefore, nothing in theology can be scientific unless we believe the fundamentals to be true—that God (or at least creator) exists, for example. So, the highest fundamental principles come from divinity in the form of revelation in its various forms.
Another theologian from the distant past, Thomas Aquinas, said, “It is necessary for human salvation that certain matters that exceed human reason be known to us by divine revelation.” All he meant is that no matter how advanced we get with conventional sciences and technology, we still can’t know the highest things that are essentially unknowable by humans. However, theology doesn't fill in the gaps of science (lest it create a weak “God of the Gap” scenario), but rather expands that which is beyond knowing through science and what is reasonable through philosophy. Using faith as a starting point, which Aquinas also called “thinking with assent,” is really the only way to actually experience the object of theology (i.e., divinity) and know anything about it. The fundamental articles of faith can’t even be disproved through denial of them. You can really only show the difficulties of their acceptance or denial.
Reason doesn’t replace faith, but unfolds from an act of faith.
Theology shares reason with the lower sciences, and divine revelation requires reason if it’s going to be of any use to us. But, however important, reason alone isn’t enough for theology, as Aquinas said, “Truths about God attained by reason alone are only attained by a few, after a long time, and with the admixture of many errors.” Nonetheless, since faith seeks understanding, without reason, faith has no further movement and becomes fideism (or, as you may otherwise know it, “blind” faith). In applying the principles of faith to reality as we know it, rationality is a rigorous and accountable means to do so. In this way, revelation both stimulates and requires the believer’s reason and rational faculties—reason doesn’t replace faith, but unfolds from an act of faith. Pope John Paul II once put it well when he said, “Faith and reason are like two wings on which the human spirit rises to the contemplation of truth.”
Theology is related to all other sciences in a sort of hierarchy by means of philosophy. The other sciences are necessary as the human spirit is both intuitive and rational, using reason to discover truths by analysis and investigation, thereby organizing those truths in a coherent fashion. So, as each science investigates its respective object and reaches to its higher science, each eventually reaches to the transcendent, which is unknowable through reason alone. Philosophy builds a bridge to the transcendent from the other sciences by mediating their application in a universal way and making them reach to theology. Therefore, there must be a healthy and consistent dialogue between theology and the other sciences, bridged with philosophy, so as to prevent theology from degrading into wild superstition or zealous fanaticism, as well as allowing other sciences to soar to the full heights of what man can know. Philosophy also allows theology to reasonably critique the validity of its assertions, thus validating it as a true science—as Albert Einstein once said, “Science without religion is lame, and religion without science is blind.”
The beauty of theology is that its investigations never come to rest.
Since the faith component of theology was defined earlier as “thinking with assent,” it also distinguishes the difference between theology and science. In science, observation leads to and finds its completion in the acceptance of conclusions, while in theology, the will commands assent to principles of faith while investigative thought processes are still underway and continue to reach for more understanding—the beauty of theology is that its investigations never come to rest. Understanding, therefore, is made possible by basic, fundamental beliefs (not necessarily specific doctrinal details). But this doesn’t mean the theologian assumes a whole lot of truths from the beginning. But, the theologian rather listens to revelation as the principles of the discipline and thereafter seeks to apply reasoning and causality to grasp at knowledge of the Creator through created things in a similar way that other sciences accept certain principles in order to logically follow causality from its effects to its source. While other sciences are self-evident or reducible to the conclusions of a higher science, theology is the highest of sciences that all other scientific conclusions seek to attain to, as its object is the highest principle that exists—divinity.