The Two Great Poles are naturally occurring phenomena which unite and express the polarities of the four polar elements.
The Weave represents the framework of the Dream in all its forms, the naturally static or standard patterns within the honeycomb of multiple realities - without which the Dream would be continually exploding and imploding. The Wheel is its compliment and its opposite, representing everything novel, unexpected and emergent - without which the Dream would stagnate and fossilize.
These forces are part of the Dream, they are the next actor after the mere fact of the Dream itself. For something of the Dream to contact the Wheel or the Weave directly is a fundamental form of sorcery and is very dangerous. Using spells, familiars and materia to access the workings of the Two Great Poles attracts less attention even though it limits the interactions possible.
The Great Poles are both antagonistic and interdependent. Sometimes, they act in concert. Again, it would be wrong to think of them as sentient. They are representative of the mechanism of the Dream, existing both to make what's new and preserve what already is. When they act conservatively they tend to interlock and act together, when new things come into being the Weave takes on the role of destroyer, trying to eradicate them, the Wheel opposes the Weave in this and thus only the strongest realities are supposed to survive.
Agents of the Great Poles
The Wheel and the Weave, like the Dream and the Void, manifest within the dream through entities and within creatures that act as avatars for their energy. Service to one or other of the great poles is a matter of preference for creatures that are not direct manifestations of them. The only beings capable of overruling the workings of Weave and Wheel are agents of the Dream itself.
While any being of the Dream may pledge to server either the Wheel or the Weave there are certain concrete manifestations that derive directly from these energies. These manifestations are filtered through the perceptions of the being apprehending them but share some unity due to the close binding they share with the originating principle i.e. if one were represented by, say, a horse it would have elements of horse-i-ness to beings who had never seen a horse because the horse thing is so closely bound into the agent's essence.
Agents of the Wheel and the Weave are quite sophisticated and vary wildly in their specific expression. This is because within their great pole each one represents four different polarities and various agents tend to play up one or other of the polarities. For example some agents of the Wheel are great proponents of the principles of life, others like to dwell upon the principle of Destruction. There is a lot of latitude in expressing a philosophy that is mostly based in the facets of one of the great poles.
Civilisations and the Great Poles
So varied are the layers of philosophical meaning allied to either of the great poles that whole civilisations can form which dedicate themselves to the glorification of one of the poles. These civilisations tend to follow a particular lifecycle. Either they rise to greatness making huge empires and then are riddled with decadence, civil war and stagnation before being replaced by another civilisation, or they rise to greatness, allow certain citizens to attain transcendant knowledge and then end up struck down by some balancing motion by the opposite pole.
More sophisticated civilisations balance parts of both great poles although these civilisations are less likely to produce anything identifiably and universally heralded as great they tend to be very hard to completely eradicate and tend to lurk in the shadows of Great Pole civilisations.