Fire is the state of matter known as plasma. This is not to be confused with "fire" as it is known on the physical plane. Unlike the other three elements, Fire cannot exist on its own. It must consume or react in order to continue. That is why nearly all of it has been sequestered in the stars: its immense energy is transmitted safely only over vast distances or doled out in minute volumes.
However, just as a planet is a tiny seed of the three elements in a galaxy of Fire, there is a tiny spark of Fire, of life, in every living thing. Fire is the final ingredient needed after the three elements have been sculpted using the tools of addition and subtraction. Reintegration of Fire is the final step on the href="theLongRoad.html">Long Road and its mastery allows one to enter the ranks of the Pilgrims and wield the Primal Force of Order.