At your request, the Golden Lord gives a surprised grunt before turning around. He eyes the amulet that you hold carefully, and puts a hand against his chest when Rem speaks of the similarity that it holds with the cogwheel embedded in him.
"Are you not a healer? How terrible the arts must have degenerated for you to be unaware...." Shaking his head, he straightens his stance. "These items we both bear are pieces of heaven, Celestial Shards. When the people of our world learned of the deceptions of the angels, we tore through their realms, destroying celestial engines and breaking apart their unholy artifacts. Celestial Shards are what remains of those powerful relics."
As he continues, there is a slight hint of a smile on his face. "But we did not destroy for the sake of destruction. Surely you have felt the power that these fragments still hold. From them, we built anew, creating marvels and machines worthy of a true heaven. True Gods were built from them, perfect exemplars of our ideals. Whole nations were granted inhuman powers. Even a single one of them contains a vast amount of divine power." His expression very serious, he sternly points at you. "Whether you decide to build something from yours, or take its power for yourselves, I would advice keeping it close until you have made the decision. Those who know the nature of a Celestial Shard are sure to covet it."
In game terms, Celestial Shards are required if you want to build Impossible artifices like floating castles or divine artifacts, or if you want to enact Impossible transformations upon mortals like granting a whole village super strength or turning them into half-dragons. You have to pay Celestial Shards in addition to the regular Dominion/Influence cost of the change you want to enact, in any case.
Alternatively, you can always just break a Celestial Shard to gain an immediate 4 points of Dominion, which you can use however you wish.