Mortals, haunted by death's spector...

"What meaning can your transient existence hold in the shadow of death? You'd stand idly by as that shine is needlessly lost to the darkness? Did you not bemoan your powerlessness as you saw your kind die out in Yaoon?

Widdershin is condescending and mocking during all other confrontations, but when you are about to face him for the final battle to save your World Tree, he is quite open about why is he doing what he is doing.

By his own description, his World Tree came into existence weak: "Gilgulim came into existence a fragile and unstable world, its lands wastes, devoid of verdure. I could only watch as life there raised a dying moan upon its first breaths. I could hear the lamentations of Gilgulim's World Tree. Mana... If only there were Mana.". Who knows how long Widdershin had to listen to his World Tree suffer, dying slowly. He begrudges death. So he plans to make a world, where death can never casts its shadow. Turning Gilgulim back into a seed was the only way to circumvent its death. But what good would a World Tree seed do, if it never grows into a World Tree?

Mormo argues that death is the natural of order of all living things, and Widdershin refuses to accept this as absolute truth. He will not only save his World, he will take in other Worlds and save them as well. By merging and becoming one with Gilgulim, they could live forever too. As it is seen by the Yunanate blossom and Septanite Nugget, parts of the absorbed World can exist within Gilgulim without being completely lost. Widdershin sees what he offers as salvation. Aurora saw Gilgulim as salvation, and at the time, so did Kanonno. He cannot comprehend why Terresia's Descender would not jump at his offer for eternal life.

He wanted more than just to save his world, he wanted a world where he did not have to see death. He intended to save all worlds, which in theory seems noble enough. What he is not offering though, is the option to become a part of Gilgulim, he is forcing his will on the World Trees, as he forced his will on Mormo's Yaoon.

The Descender's entire purpose, the very reason a Descender is created, is to save the World Tree. Descender's are not human beings, they were born directly from the World Tree, as a form of defense. Though it was extreme, Widdershin was doing what he was created to do. He loved his World Tree, and in a way, loved the World Tree's of other world's so much so that he did not want them to have to suffer the agony of having to watch the World Tree die, and consequently the world, die.