"Domain Cores & Pillars"
The holy spirits were only there in Heaven because these people didn't enter the reincarnation system and chose to live forever in the form of a heart.
With the nourishment from Heaven itself, their souls would remain intact, and these people could always serve Heaven as holy spirits.
Gabriel was the overlord of the holy spirits, but even so, holy spirits were rarely involved in the main battle between Heaven and Hell.
Because of this, the spirits mainly went to various places to answer the summon of Gabriel's consciousness with their true bodies.
The celestial ancestors that Queen Rachel summoned wouldn't really die even if they died in this domain, but the creatures and spirits that came out of the Gate of Heaven and the Gate of Hell would die for real.
Gabriel's consciousness could summon up to a few high-level holy spirits entirely because there were so many spirits in Heaven every year.