5e Planescape: Tales of Devotion
The Three Rules
Despite the infinite variety of the planes, some rules remain constant. These are the three principles which one is required to understand in order to be able to operate and survive on the planes.
The Center of the Multiverse
Because the planes are infinite, each and every place has equal claim to be at the centre. No place is more important than another simply because of its location or size because wherever a place may lie, an infinite expansion surrounds it on all sides. Each and every person is similarly situated, but just like some places are more useful than others, only what one makes of themselves gives them any value.
The Unity of Rings
The multiverse itself is structured on a number of rings, from the Elemental Planes to the Great Road connecting the Outer Planes. Even Sigil itself is a ring. Consequently, each and every trip around a ring eventually connects with the place where one started, and each round remains the same.
Rule of Threes
Everything comes in threes – the good, the bad, and the ugly. Whenever there are sets of two, the third thing which complements it simply remains to be uncovered. Number three holds great power on the planes.