Piety

Power of the Gods

Based on the rules presented in Chapter 2 of Wizard's of the Coast's Mythic Odysseys of Theros

When a hero is strongly devoted to a particular god - be they a general champion of that deity, a cleric, a paladin, or just an extremely religious person - that god may bestow magical powers upon the character. These rewards are awarded via piety.

Gaining & Losing Piety

When your character chooses to be devoted to a particular deity at character creation, their piety score for that deity is 1. Whenever your character does something to advance that deity's interests or goals, make a great personal sacrifice for them, or otherwise performs a great deed in their name, the DM may award your character piety (usually only one point at a time).
If your character ever works against the interests of their god, or otherwise opposes them, they might lose piety (typically also in increments of one). Furthermore, characters can reject their divine patron and instead take up the worship of another deity, in which case you lose all piety and associated benefits from the abandoned god, and start at 1 piety with your new god. Characters who aren't devoted to a particular god might acquire charms, gifts, or boons from spirits, warlock patrons, or other supernatural entities. Alternatively, a character might argue against the exaltation of any gods, in which case they might have the Iconoclast supernatural gift - or they might be an oracle of their deity, giving them the Divine Oracle supernatural gift. Both supernatural gifts can be found in the first chapter of Mythic Odysseys of Theros.

Benefits of Piety

Once your character's piety score is at 3 (and again at 10, 25, and 50) their deity grants them favors of increasing power, related to their divine domain. If your character's piety score reaches (or exceeds) one of these thresholds, and then falls below said threshold, your character loses the benefit of that tier. The aforementioned Divine Oracle gift replaces the abilities a character would receive from piety, but they still gain piety in the same manner.

Piety from a Pantheon, Philosophy, or Force

Just as clerics might serve a whole pantheon, a particular philosophy, or the manifestation of a cosmic force rather than an individual god or goddess (see Xanathar's Guide to Everything, page 18) and paladins swear an oath to uphold ideals, not necessicarily the will of a particular deity, sometimes piety might be awarded for a character's devotion to something other than a deity. Throughout this article, piety is referred to as coming from a god, but if your character doesn't serve a god, the article should instead be read as referring to whatever divine force your character serves. This option might be particularly useful to paladins and monks - who often uphold ideals and philosophies, respectively, rather than deities - but can of course be used by any character of any class.
A good example of such an alternative in Matelo Kaloje would be the philosophy of the Followers of Raan from the The Raan Dynasty. Alternatively, a character could be devoted to the whole of (or just one clan of) The Moradinsamman rather than an individual deity from the dwarven pantheon.