The world is caught in a battle between vast cosmic forces; the largely benevolent Powers That Be, ranged against the Old Ones. The Powers appear to be broadly in favour of humanity, the Old Ones in favour of the return of the earth to demonic rule. While the exact nature of these two conflicting forces is unclear, it is known that they do not reside in the mortal reality, and that their war is primarily fought through chosen champions (I Will Remember You). Certain individuals are chosen, either by the forces themselves, or by some overarching cosmic destiny, to lead these two sides - the mortal and demon worlds - in the fight.
The generic term for the forces of light and order is The Powers, or The Powers That Be. They and their direct servants clearly wield tremendous power (I Will Remember You), but they do so only based on their own, usually highly opaque, reasoning. Whatever the true extent of their power, they fight using proxies and champions, just like the Old Ones. They are also plainly not omnipotent - or if they are then they chose, again for their own reasons, not to exercise absolute power - otherwise the battle against the Old Ones would be less than a formality. Nor are even their most powerful servants invulnerable (To Shansu In LA). While they are The Powers That Be, it is far less certain that they are necessarily The Powers That Were or That Will Be.
The Powers do not exactly seem to be good, at least not in human terms. They seem to represent order and light and the good of mortal creatures, but they are distant, remote and dispassionate, communicating with their servants through intermediaries and visionaries (City of Angel, Through the Looking-Glass). Even a connection as indirect as the visions sent first to Doyle, and then to Cordelia, is unusual, as shown by the gift's importance to the Covenant. The fact that the Covenant desired a direct link to The Powers also casts some doubt as to their inherent benevolence.
The Oracles represent - or represented - one of the most clear and direct links to The Powers. Access to them was denied to most, including messengers of The Powers, but Warriors were permitted to enter their sanctum. Unfortunately, while they possessed a direct and fairly immediate connection to The Powers, they were consequently further from humanity than the usual messengers. They were thus rather obscure, and their motive and motivations were arcane. Whether their obscurity - and that of The Powers themselves - is due to a deliberate choice, to some rule binding even they, or simply to their inability to truly understand the human mind, is unclear. While they had access to great power, the Oracles proved unable to directly oppose a Warrior, and were slain by Vohca.
The Spirit Guides are another force able - yet unwilling - to reveal great secrets (The Zeppo). Dwelling beyond life and death, they know much that is hidden, but conceal their knowledge from the living in all but the most exceptional circumstances. They do so because their knowledge is not meant for those who still walk upon the Earth.
The nature of the 'opposition' is as unclear as that of The Powers themselves, but they have Soldiers, and so presumably must have some kind of focus and will. It is quite possible of course that The Powers are their own opposition, and that Good and Evil are meaningless to them. The existence of The First Evil suggests that the latter is not the case, but the fact that the Covenant desired the True Sight for their own purposes suggests that a link to The Powers might serve either good or evil ends.
The Old Ones is a term used by the Brethren of Aurelius - among others - to describe the beings that they worship (Darla), while D'Hoffryn, whose ability to transform a mortal into a demon suggests a very high level of power, refers to his own kind as 'The Lower Beings' (Doppelgängland, Something Blue). The latter is also used, however, by the Oracles to describe both Angel (I Will Remember You) and Vohca (To Shansu In LA). Whether it then refers to demons in general, or is a general term of disdain, is not clear, so 'Old Ones' is used in preference here.
It is of course possible that there is no unified opposition, just a collection of demon warlords and hellgods, some greater and some lesser, and all bickering among themselves as often as warring against The Powers. In such a case, Wolfram and Hart's 'Senior Partners' (Reprise) might represent one of these factions; D'Hoffryn's circle of Lower Beings in Arashmaharr another. A third power block might consist of the rulers of Glory's world (Spiral) - first the triumvirate, including The Beast, later her two co-regnants without her - and a fourth the powers worshipped by the Covenant (Through the Looking Glass).
If these groups war against each other, then we can even begin to see (and note, when I say 'see', I mean 'invent') arcane motivations in their actions. For example, D'Hoffryn refuses to return Anya's powers to her, not only because she has 'proved unworthy', but because she would hand a major victory to the Master's sponsors. Alternatively, he might know through some prescience that she would be the one to give the Slayer the key to defeating The Beast. That D'Hoffryn later returns to freely grant the return of Anya's powers of course supports the theory that he had a hidden agenda in denying her before.
The fact that such connections can be invented is of course the mark of a well-developed universe.
While The First Evil (Amends) is plainly powerful, it does not seem to be a mover-and-shaker. Rather, it is guided by its Harbingers, and does not seem to work well with others. It has great mental powers, but does not seem to possess the ability to directly harm a physical being. For all its posturing, The First is unable to actually strike at Buffy.
It may be of course that what attacked Angel was a mere emanation of The First; a projection called forth by the Harbingers to act on the Earth, and that The First itself remains in some hellish world, plotting and scheming, and sending forth its minions across the world. While Angel's fall, and through it Buffy's destruction - or perhaps Angel's destruction, and through it Buffy's fall - might then seem a somewhat trivial cause for such a being to lend a direct manifestation to, given later revelations about Angel's role in the coming apocalypse, and Buffy's part in preventing countless Armageddons, and the collapse, even temporarily, of the barriers between the worlds, then they can no longer be seen as just two more Warriors. Rather, each possesses - or perhaps is possessed by - a great, singular and unforgiving destiny, very likely to draw such auspicious and deadly attention.
The Warriors are the premier champions of the great forces. As the name suggests, they usually seem to be highly skilled in combat, but while physical confrontation is their principal modus operandi, they also tend to display wisdom and cunning. Being destined to play a role on the front lines, these Warriors tend to find themselves in the thick of battle without even trying. They may or may not know what they are destined to be, or what higher cause their efforts serve, but their actions will almost inevitably lead them to their destiny. Of all the servants, Warriors have the most glamorous role, but frequently the most arduous. As the ones on the line, it is the Warriors who have to make the hard decisions, and the tough sacrifices. A Warrior's action almost always have far reaching consequences, and a clash of champions - such as Buffy's duel with Angelus, or Angel's battle against Vohca - will often shift the balance dramatically in the ongoing war.
The Warriors who champion the PTB are noble heroes, pure of heart. They are usually fighters, pure and simple and without pretensions, but they are also expected to be leaders and planners (Graduation Day: Part 2). They are seldom flawless, and indeed the Powers often seem to like a little bit of the darkness in the ones they choose to fight it. While it may seem reasonable to assume that the Slayer is one of these Warriors, it is possible that not all Slayers truly bear this touch of destiny. The Slayer was, after all, created by human agency for human purposes, and the heritage is neither granted nor guided by the PTB.
There is little doubt however that Buffy Summers is a true Champion, as is Angel, the vampire with a soul (I Will Remember You). Both have displayed all of the necessary qualities, and feature highly in the exciting world of prophecy (Prophecy Girl, To Shansu in LA). Less likely Warriors of the powers have included a Pria Motu warrior-demon, again supporting the idea that the Powers have a liking for converts to the cause.
The Warriors of the Powers find themselves tested with great frequency, both by their foes and by their own patrons. They rarely receive aid from on high, and never without first proving themselves deserving. When nothign else could have done it, the Powers seem to have sent the snow-clouds which blocked the sun and kept Angel alive, but only because Buffy was prepared to fight to keep him alive (Amends). For the most part, Angel has to fight from the shadows, like any other vampire.
Champions of good and order also face the challenge of acting as defenders instead of aggressors. As well as vanquishing the darkness, they are required to protect the innocent, where the enemy care little for friendly casualties and less for bystanders. Those who forget this part of their purpose risk falling into darkness,and taking the world with them (When She Was Bad, Becoming: Part 1, Judgement, Epiphany). For the Soldiers of the Light, there can be no simple victory, no end of the line until they lay aside their burden in death; there is only the constant and unending struggle.
The Warriors of Darkness seem to get better breaks than those of the Powers. Not only are they mostly demons, they seem to be considerably more tooled-up. They are targeted at the Warriors of the Powers, given access to potent and blasphemous magics and all the best toys (To Shansu in LA), and in general appear well-informed as to what they are fighting for and what their part in it is, while Warriors of the Powers have to put up with cryptic visions and more cryptic prophecies. In addition, the Soldiers of Darkness rarely have to protect anything, only to sow chaos and destruction. In some ways, the battle between the champions of the Powers and the Opposition can be likened to a football match, in which one team is deemed to win f they burn the stadium to the ground, while the other must play by the rules.
The Master might have been considered a Warrior of the Old Ones (Prophecy Girl), as might Angelus in his 'raise Acathla, destroy the world' phase (Becoming). In fact, Angel's career as a Warrior probably begins with his recruitment by Whistler to prevent the rise of Acathla. When Angelus returned, he remained a Warrior, but for the other side. In his earlier career as Darla's paramour and partner in chaos, Angelus was too petty and limited to be a true Soldier, his deeds - while admittedly horrific - serving no greater purpose than his own satiation. After regaining his soul, he remained unfocused and pathetic, until he made the conscious decision to protect Buffy and make something of his existence.
Vohca was explicitly named as a Warrior of the Underworld (To Shansu in LA) - and presumably serves the same masters as Wolfram and Hart - as was the Mohra demon (I Will Remember You). The Judge (Surprise, Innocence) is another maybe, while Adam (Primeval) probably was a Warrior, but not for the Old Ones.
Warriors are not the only servants of the Powers; many others serve in their own ways. There are messengers, like Doyle and Cordelia, who serve as a connection between the Powers That Be and their Warriors, and support personnel, like Wesley, Gunn, the Scoobies, or indeed the Watchers. Many of these individuals are accomplished fighters, or possess other valuable skills or magical powers, they simply do not bear the burden of destiny as the Warriors do. This is not to belittle them, as these people frequently play a vital - sometimes indispensable - role. Just because you are not a Warrior, does not mean you do not count, or that you can not make a difference. Everyone plays their part, and anyone can be a hero in their proper time (Hero).
While it is as mysterious as anything else to do with The Powers, it is implied that the Pure Sight is not only very rare, but is valued both by Servants of The PTB, and by the other side (Parting Gifts, There's No Place Like Plz Grb). It is not merely an ability to foresee the future, but rather it represents a direct - if rather obscure - link with The Powers. It appears to function as a means for The Powers to contact certain of their Warriors, as with Angel, and to guide them in the fight against the forces of darkness. It seems most likely therefore that the vagueness of the messages given through the Sight represents not deliberate evasion on the part of the PTB, but rather an inability to directly express their needs and wishes. The Pure Sight seems keyed primarily to pain and suffering (To Shansu in LA), but when guided by the powers it specifically presents the bearer with images of situations in which they or the Warrior whom they accompany can make a difference.
Also, the Sight can apparently be passed from person to person, usually being held by a hybrid demon. The burden is more than most pure-blooded humans can physically bear, and it seems that a hybrid's demon side can absorb the Sight from a human carrier given appropriately intimate contact. While the Sight is a link to The Powers, it can also be manipulated by the forces of the Old Ones, opening the bearer to all of the pain in the world, to their undeniable detriment (To Shansu In LA, That Vision Thing).
The law firm of Wolfram & Hart is but the latest incarnation of an ancient darkness (Reprise). Under the guidance of their infernal Senior Partners, Wolfram & Hart represent, feed upon and foment greed, misery, fear, jealousy, hatred and suffering, both human and inhuman. They have their share of demonic clients, but their primary interest appears to be in the strife and violence which arises between humans.
More so than any other servants of the Opposition, Wolfram & Hart do not care if they win or lose. The lawyers who are their primary asset obviously want to win their cases, make lots of money and retire rich and comfortable, but to the firm, and to the Senior Partners, what really counts is that the battle is not only fought, but perpetuated; that the good are hounded, and that as many innocent victims as possible are made to suffer. Wolfram & Hart's victories come not from the destruction of Champions of the Light, but from the violence, paranoia, betrayal and compromise of humanity.
Buffy: So what are you? some kind of immortal demon sent down to even the balance between good and evil?- Becoming.
Whistler: Wow. Good guess.
The character of Whistler (Becoming) presents us with something of a conundrum. As best we can tell, he is a full-blooded demon, who acts as a messenger of The Powers. His motivation is not a desire to do good, however, but - by his own claim - to maintain the balance between good and evil. While his appearance is brief, and his place in the original draft of the Angel pilot casts him as a vision-afflicted half-breed like Doyle, the shooting script for Becoming makes his original role clearer.
Whistler is there - as Buffy surmises - to keep the balance by ensuring that the Old Ones never gain the upper hand and destroy the world. His on-screen role is specifically to restore Angel to a semblance of dignity in preparation to fight against Acathla. He is plainly gifted with - or has access to someone gifted with - some sort of prescience, but his source is not 100% accurate, as they did not foresee Buffy's influence on Angel, and the resultant fact that he would lose his soul, and be the one bringing Acathla forth, not fighting against his restoration.
The fact that there is someone who works at keeping a balance suggests that the victory of good might not be any more desirable than the victory of evil. What this might in the end mean is uncertain, but the implications of the result of the banishment of all the demons from the world (Fray) is that without an external threat, human greed, avarice and cruelty would rise to new levels, creating new forms of evil to replace the absent demons. In such a world, the likes of Wolfram & Hart would flourish - even bereft of their supernatural patronage - and human darkness would eclipse the memory of demonic predations past.
While the Buffyverse may not be the best of all possible worlds, it is not the worst either.
The Initiative are unusual participants in the great conflict, because they seem to represent neither light nor dark, but a sort of grey area in between which is yet not the kind of balance espoused by Whistler. Although self-consciously humanist in their outlook, their motivation is not truly moral. The foot soldiers may be in the game to defend the innocent - or the American Way - from the monsters, but their final loyalty is to their superiors, and the Initiative itself is not about protection: it is about knowledge and power. It represents a classic example of amoral patriotism - my country right or wrong - and cold science - any sacrifice in the name of progress. The work of the Initiative represents a sacrifice of its members' humanity in the name of humankind; a sacrifice which in itself renders the goal meaningless. The cause of humanity is here invoked in vain, to justify the things that the Initiative does essentially because it can.
The callous manipulation of the Initiative's own soldiers - psychological as well as biochemical - without their consent or knowledge, in the name of the cause, highlights the nature of the Initiative: Not evil, nor good, but cold, calculating and precise. Between the angels and the demons, they are the machine; ordered, disciplined and perfect.
As scientific demon hunters, the Initiative operates in a constant state of cognitive dissonance. They label demons as HSTs - Hostile Sub-Terrestrials - and consider them little more than animals (Hush). While they monitor hotspots of otherworldly energy, they fundamentally do not believe in magic (Primeval). Their goal is to bring demons, magic, and all other matters paranormal out of folklore, and into the rigorously controlled realm of scientific knowledge; to label and codify, and give things names (Restless). By doing so, they believe that they will bring these things under their control. The Initiative operates at the forefront of the battle between man and supernature - making little moral distinction between different supernatural occurrences (New Moon Rising) - and attempting to make the world safer and more stable by harnessing the lightning - as it were - for the benefit of mankind.
At the heart of the Initiative is 314, the project aimed at creating the ultimate Warrior of the Machine: Adam. Adam is dispassionate, analytical and precise, driven not by malice but by enquiry; the epitome of the Initiative's coldly scientific goals. Unfortunately for his creators, Adam too perfectly represents the Machine. For a being of his power, loyalty to human goals is wasteful, and so he has none. He understands honour implicitly, but has none of his own, even if parts of him were a boy scout. His only drive is towards a state of perfection, and he has no compunctions about any action which leads to that goal.
Adam sees the world as it is at its most basic level: atoms, molecules, forces; devoid of emotional context. Hence he sees his destiny in the remaking of things from the ground up, without concern for the pain he might inflict. Pain to Adam is an irrelevance, a simple stimulus, to be noted but not obsessed over; fear and anger, and all other emotions, are likewise nothing but curiosities.