The motes of Essence in a god's possession are it's very life force. When a god spends motes it feels weary and when it has a full Essence pool feels lively and energetic. If a god spent all it's Essence it would no longer exist as an Essence pattern and fade away. When a god (or another spirit) does when it spends Essence is spend itself. Gods have peripheral Essence pools which they can spend with obvious effect. They can also spend Essence from their Personal Essence pool but it's not something a god does lightly. They are spending the Essence that makes up the core of their being. By spending Peripheral Essence they're also spending part of themselves but less important outer layers that can be more easily spent and recovered. Worship is so important to gods because people are spending their valuable motes dedicated to the god itself so that Essence becomes part of the god's form. For every day of dedicated worship to the god they recover a number of motes equal to the Magnitude of the group praying to them. This is why Creation often holds day-long festivals. If a group taking part in dedicated worship has an Essence greater than one multiply it's magnitude by their Essence. Enlightened human priests are often separated into different castes according to their spiritual advancement. Such priests spend virtually every day of their lives in devotion and directing the worship of the masses.
Demons often promote just enough of their servants to induce hopes of betterment to keep their underlings loyal.
