Celestials are beings of great power that controlled some aspect of mortal singularities. Worshipers were necessary for the survival of a Heavenly Dweller and the powers. The number and zeal of the worshipers largely determined the power of the Celestials. If the popularity was waning or there are no suitors, the power fades and in extreme cases they can die of neglect. When these gods from the celestial pantheon and beyond cross with mortals, you get Demigods.