The Essence Stone is said to be the First Talans standing place when he underwent his conversion at the Well of Essence. All young Talan look forward to standing upon this stone when they undergo conversion.
The stone was stolen by Kroax, he believed that if he prayed with it in the Temple Fae, he could convince the Yod Fae to deliver him more soldiers during conversion!
In truth, the caretaker who was watching the Well of Essence at the time had anticipated that Kroax would take the stone, thus he had a copy made and hid the original somewhere dangerous! Thankfully it seems that Cutter Slade was able to retrieve the stone!