Sapphire and Steel speculative headcanon. Spoilers present.
What are the transient beings and why are they sometimes spoken of as a higher power?
Where do Sapphire, Steel and their colleagues get their assignments?
Why and how were the transient beings limited to travel into the past?
What is time?
Time has a dual nature. There's time in the ordinary sense and Time the entity. Plain time which passes and Time which is imprisoned, always trying to break free, seeking to destroy.
Time, then, it's entropy made manifest. This, I suggest, was the creation, possibly unintentional, of a certain group.
The transient beings.
Entities like Sapphire and Steel may not be invulnerable, but they appear to be otherwise immortal. There's a suggestion, at least in the radio plays, of their being reincarnated as necessary. They are subject to to passage of time but have freedom of travel and are not subject to entropy.
To be transient is to be subject to entropy. Mortal.
In the final television adventure it seemed that, in at least one case, Sapphire was unable to determine whether one of the transient beings was in fact so. All appear human and this may be more than a visible resemblance.
I suggest that the transient beings are human. Possibly modified, humans from a far future. Nihilistic, bitter, resentful of their ancestors for subjecting them to the entropic future.
So they determined to extinguish humanity, rather than endure the dwindling embers of time.
They created, through advanced technology, Time the entity. The embodiment of entropy which they would unleash on a young humanity. But they did not account for, were not yet aware of, the forces that regulated reality.
Enter the elements. No doubt present since the beginning of time, at least in the case of hydrogen and helium. We never met them of course, but who could be a more senior element? Here then is the source of assignments.
Although hydrogen is the more fundamental, I think helium the more authoritative. Also primordial, but even less impacted by the passage of time. Indeed, Helium may be the head of a group of elements which do not react, do not change; the noble gases. A noble council, if you will.
Over the course of time new elements would be born. Both literal, physical elements and their counterparts, the personifications thereof.
Obviously, neither Sapphire nor Steel are actually elements. Exploring their nature is a little beyond the scope of this particular bit of nonsense, suffice to say that the fact that they respect life and try to preserve humanity may be important to that.
I think that the "higher power" of the transient beings is actually... humanity. Sentient, mortal life. Creative, innately valuable, the very thing that the elements seek to preserve.
So the elements contrived to limit the transient beings to retrograde travel and to imprison the embodiment of entropy, just as they address all irregularities—of human origin or otherwise. The two actions are probably intertwined. But even so, they hold their opponents' essential humanity in high regard. This creates a tension terrible to endure.
