It is my contention that the theological and mythic elements of religion are best understood as prescientific (or a-scientific) systems analogous to the reality-models used by both philosophers and scientists. That is, historically, the various systems of divine ontology are best understood as nonscientific methods of explanation for the nature of the visible world. Religion, as such, is wider in scope than mere ontology, however ontology (along with the attendant myth-cycles) is certainly one of the two* fundamental elements thereof.
The various ancient polytheisms develop around an axiomatic core of interconnected interplay between the elements of creation. In other words, there is a basic assumption that a coherent story can be told encompassing the totality of observed phenomena. Such a coherent story is known as a myth-cycle. The regularities observed in the world are due to the collective activity of the divinities, whose mythic and cosmic dance is the underlying cause of the rationality (and irrationality) of creation.
The fundamental unit of the polytheistic system is the pantheon (Greek = “all the gods”), or the governing set of divinities. The divine pantheon, as a collective entity, is responsible for maintaining the rational (and irrational) structure of perceived reality. Individual divinities are delimited through coherent groupings of characteristics/spheres of provenance. These divinities and their activities are interpreted anthropomorphically, in order to achieve a mythic vision relevant to the human condition.
Monotheism, as a theological development, received its primary impetus from philosophers** who were concerned with determining the “first principle”, a single element/idea from which all things originate. The determination that there is (or should be) such a principle is fundamental and axiomatic to the monotheistic philosophies, but its justification may be held as a consequence of a prior axiom of simplicity.
Common to both the various polytheisms and monotheisms is the idea that the visible world owes its characteristic be-ness to the activity of the divine. Common to both is the idea that divine activity is cosmic in scope, in that the entirety of visible reality is thereby sustained. Common to both is the idea that divinity is conscious (or meta-conscious), and that the activities of human beings are relevant to the divine order.
The various polytheisms and monotheisms all hold that the activities of humankind are participatory (or at least can be participatory) in the cosmic order. This attitude colors both the practice of solemn ritual as well as the proscription of taboos. The former seeks to amplify/reside in the sacred order, whereas the latter are interpreted as violations thereof.
In philosophical Hinduism, both polytheism and monotheism can be simultaneously posited, by allowing for differences in the scale/magnification of resolution. In fact, the two viewpoints are not opposed to one another, as is often thought.
Regardless of whether one is considering a polytheistic system, or a monotheistic system, or a hybrid system, the common theme is that the divine ontology acts as the fundamental explanation for the observed regularities of the visible world. In this fundamental sense, then, the development of an ontology of divinity proceeds from the same concern that drives both philosophy and the empirical sciences (at one time called “natural philosophy”). Obviously, however, the methods of determination involved in these three sibling areas are quite different - with the pure empirical method (hypothesis testing) of science being considered the best (most informative; most useful) currently.
Proponents of theology often state that divine ontology can provide justifications for the meaningfulness (mythic relevance) of experience which science, due to its detachment of subject from object, and its categorization-analysis, cannot. On this point, I am inclined to be in agreement, preferring not to grant exclusive truth status to any model.
*The other fundamental element of religion, namely the transformation of the self toward the divine prototype, is not examined in the present analysis.
**Here, I am indicating the ancient Greek, Arab, and Indian philosophers who proposed the various monisms in ancient and medieval systems. Though both the Hebrews and (briefly) Egyptians had developed non-philosophical monotheisms, these systems were limited in their influence in the ancient world.