Once each Spirit Deity reached the four-yānas sector of the Land of Death, they must cultivate by creating their own Spirit Deity Seal.
They would use the level-four Spiritual Garment as their origin power. This was why choosing a Spiritual Weapon for creating a Spiritual Garment was so important.
The stronger that Spiritual Weapon, the more powerful the Spiritual Garment.
The secret of breaking through the four-yānas sector was to use the Spiritual Garment to break through the celestial stage, using all one's powers to break through the boundary between the three-yānas sector and the four-yānas sector by oneself.
This sounded easy but was actually difficult in practice.
Otherwise, Spirit Deities would be easily found all over the realm.
Moreover, the youngest among the current Spirit Deities was several hundred years old; the oldest was around thousands of years old. They were ancestors of their own families.