Simplify the following text for a Grade 9 native English-speaking person.
Original: CR ritual structures are based on the ancient Celtic idea of the `` Three Realms '' - Land , Sea and Sky - with the fire of inspiration seen as a central , uniting force .
Simplified: The ancient Irish swore their oaths by the `` Three Realms '' - Land , Sea and Sky . Based on this precedent , reconstructed Gaelic ritual structures acknowledge the Land , Sea and Sky , with the fire of inspiration as a central force that unites the realms .