Board Thread:Lore Discussion/@comment-92.232.8.150-20140601154723/@comment-25047024-20140601164900

Kagrenac's plan was to merge all Dwemer souls into a single "Oversoul", which would become the Skin of Numidium. He did that by using the three tools, Keening,Sunder and Wraithguard at the Heart of Lorkhan. However, his plan was flawed, since not all Dwemer souls were merged into a single Oversoul (evidence being that Yagrum Bagarn is still alive in Morrowind). This, combined with the fact that Numidium was later destroyed by the Underking, erased the Dwemer souls which were Numidium's skin at the time.