Unlike other worlds in the Dungeons & Dragons multiverse, Therafim does not have any figure that might be called a "High God" or "Overgod." Io, the First Dragon, is the initial creator of Therafim, and s/he is quite removed enough from mortal life to command respect. It is acknowledged, since nothing springs from nothing, that there are other worlds out there, and other gods, and almost certainly a parent deity from whom all the other deities, like Io, come, but most of this is speculation, and a subject for theoretical academics rather than theologists.
However, the gods of Therafim (as well as godlike powers, like demon princes and high-ranking devils) are unable to influence the Prime Material Plane of Therafim directly, because of the joined efforts of Matra and Umnos (Mother Earth and Father Time, basically), who are more powerful than any other deity on the planet, in terms of god versus god combat, because of their especially close relationship to the makeup of Therafim itself - they are embodied principles of the world of Therafim itself, rather than the children of deities, former mortals elevated to divine status, or embodiments of lesser concepts. Normal-level outsiders are not even allowed on Therafim without being called there by mortals, and it is an act of blasphemy against Matra and Umnos for them to stay longer than to fulfill a single, specified task (within reason, of course, the upper time limit on such tasks generally being the lifespan of the mortal who summoned them). Druids and paladins (neither of whom usually worship deities, but are rather most often free agents, working to further the goals of keeping the balance of nature or of good and evil, respectively), especially, consider it a part of their holy task to hunt down and destroy all such blasphemers, and good outsiders won't linger on the Prime Material Plane for long, knowing how it disrupts the balance of the world, though chaotic ones might hang around for longer to pursue a specific, very important goal. The undead and the deathless, being manifestations of the forces of the Negative and Positive Material Planes, as well as those from the elemental planes, are often considered abominations because of their planar interference, though less so than outsiders because of their close ties with the workings of Therafim's Prime Material Plane. For this reason clerics of various deities can act against the once-living or elementals, either commanding or banishing them, depending on their worship leanings. The only exception to this rule against outsiders are the Inevitables, so long as they are acting under the direct command of Umnos in fulfilling their various functions of enforcing the laws of Therafim, though even Inevitables are only allowed on Therafim's Prime Material Plane in exceptional circumstances.
Because of their inability to directly influence events on Therafim (a matter that was settled in the ancient past of Therafim, as the gods and outsiders were once able to interact with the mortal world directly, before Matra and Umnos took up their posts), the gods of Therafim are forced to use their mortal servants to accomplish their goals on the Prime Material Plane extensively. Because of this, clerics are considered very important indeed, and so are often given a fair degree of freedom in their decisions, rather than being dictated to on every point, though individual deities might be more or less strict about this issue. For this same reason, ur-priests (from The Book of Vile Darkness) are considered especially vile, making them an NPC class only, because they steal their power from not only the gods, but the very forces that bind the planar boundaries of Therafim together - Matra and Umnos! This prestige class was originally taught to the world by the Dark One, who seeks to undo all of creation into a state of perfect, annihilated order, and it still appeals strongly to darkly-turned academics and those who have lost their faith in deities for one reason or another, including willful atheists.
There are also terrible, ancient powers that are not considered a part of the natural order, and yet still seek to press their way into the workings of Therafim. These are the Outcast Gods: Frenzy, the Nightmare King, Tharizdun, and, of course, the Dark One. These deities are also generally only worshiped by NPCs (especially monsters), because they are keepers of dark and forbidden lore, and their end goals will eventually lead to the destruction of Therafim itself, rendering it frozen in static order, reveling in orgiastic savagery, struck into the oblivion of madness, or dragging it back into a state of primordial chaos. Alienists (especially the Prestige Class of the same name), warlocks, and various scholarly workers of magic might carefully tread on the boundary of interaction and experimentation with and investigation of the power of such dark, primal, ancient powers as these, but to deal with them directly is to invite (if not to beg for) permanent derangement.
On Therafim, there is far less ambiguity about what the gods do and do not love, as they are an active and very real presence, and almost all communities will have some worker of divine magic of at least limited power, in the form of adepts, clerics, and druids, besides others. While the gods do not provide magic to the world (that is an inherent part of Therafim itself, and part of what makes it such a highly-desired prize by so many forces), they are able to channel it to their worshipers in a controlled fashion that is far easier to gain and safer to use than the arcane energies wielded by wizards, warlocks, and others. Thanks to this high prevalence of divine magic on Therafim, the world is quite a different place than Earth in similar medieval times, with far less disease, higher rates of birth, and far healthier people in general, which has allowed all the races of Therafim to be vastly more productive.
This is just as well, of course, because Therafim is also an incredibly dangerous place, the raw forces of magic and creation still rampant in the world leading to similarly enhanced health and rates of birth among monstrous creatures, which are a constant menace. These raw creative energies are also at work inside the world of Therafim itself, causing mineral wealth to gradually regrow in their veins, provided that they are carefully tended (a regular task of druids in the Underdark of Therafim, especially among the dwarves), and so there is more than ample treasure on Therafim, for those who are willing to take the risks necessary to acquire it. With the combination of great danger and vast treasure, the strange class of people generally called adventurers are a necessity on Therafim. The gods of Therafim approve of these unknown elements, though they are also wary of them, because of their capacity to work so much change, and so adventurers are considered a prime prize for the gods, and they are often given special consideration in the granting of powers and when exceptions are needed to explain their behavior.
The deities of Therafim are what they are, and they are the final forces to whom all those on Therafim must answer when deciding one's fate after mortal life has finished. Mortals are their agents on the Prime Material Plane, and their energies draw directly from the power of their worshipers' faith, as well as the raw creative potential that is a part of Therafim itself. While some may be less faithful worshipers of the gods than others, there are none except the willfully self-delusional who would deny their existence and the power and benefit that they bring to Therafim and its peoples. Because of them, the world is a better place. Without them, Therafim would be a far less wonderful place.