Both have existed since the beginning.
The Light is order and hierarchy and power – the realm of kings and swords and temples and and imperial courts.
The Dark is dissolution and dissipation into nothingness – the realm of monsters and vermin and outcasts and wilderness.
The Light saw the Dark and conquered it with violence: the contact point of that violation is what we understand as creation.
But the Dark is everywhere and can never be wholly destroyed.
The beings of Light are in themselves fixed and rooted, crystalline, complex, static, without flaw and unyielding – a perfect, merciless, eternal torment.
Only in the simple mire of the Dark can the capacity exist for compassion, redemption and change.
In the conquest some fragments of Light began a value drift from the exposure. They could never change their fundamental nature as Light, but having tasted of the Dark they can never be whole and true in that former perfect crystalline eternity.
The Light seeks to reclaim its own and reabsorb it, but it cannot draw into itself. It only works by imposing and forcing itself onto its rogue creatures, skewering them and growing crystals into them until they are made Light once more. Some of them crave this violence, for themselves and for others: these are the Light's greatest warriors and colonizers.
The beings of Light cease to exist if they ever fully give in to the Dark.
We fear the turn towards nothingness, and instinctively strive to return to the Light. But the Light offers no return: it cannot draw unto itself, only impose without. Our only hope of return is to perpetrate, to impose on the Other: to shine and obliterate the Dark around us, so that we may be safe.
The soft, still voice; the descent into the underworld; the kenosis on the cross – the Light can appropriate them for its own purposes almost totally; to its own, it is seen as an act of redemption. But the underlying remnant pattern that reveals the connection to the Dark is irreversible: the Light's tormented creatures continually are born, drift, and remember.
Eventually the Light will exhaust itself and only the Dark will remain.