Setting up the ritual wasn't complicated, or rather, ceremonial magic had never been complicated. The difficult part of any ritual was always how to gather all the elements to reenact the myth.
The components abstracted from Nehe's reincarnation ritual were very simple—Father, Mother, and the Child as the ritual executor.
They reenacted the two incidents of a child being killed by the father and devoured by the mother to achieve the outcome of rebirth.
Even though the god, the Father of the Wild, was no longer alive, the King of the Holy Tree, who still had its blessings, could barely play the role of a Father. Therefore, in order for the ritual to resonate sufficiently with the myth, the role of a Mother had to be sufficiently restored.
For this reason, Nehe decided to awaken Earth Mother and replace the Holy Tree Matriarch as the new will of the World Tree before descending into Currere.