Piety is one of the four main forms of currency in Crusader Kings 3. It is a measure of your character's devotion to their faith. It determines how many other rules and characters in the game see you. For example, suppose your character is from Ásatrú. There is a good chance that a good majority of the characters of the Catholic religion do not like your character more because they regard those of this religion negatively. It can be a vicious cycle when trying to engage other leaders politically. Yet, if you improve your relationships enough, this is sometimes overlooked. It is a useful tool for expanding your empire and promoting your character's faith to others.
You must first learn more about the principles and doctrines of your faith. To do this, you can visit the faith page in the lower left part of your user interface. Next to the culture icon next to your character portrait, it should be right next to your character portrait, represented by the candle. Click on it, and it should say which faith you are at the top. There is a lot of information here, outlining what you want to follow and what you can do to support your religion. Each character has a monthly piety gain, as does currency and prestige. By following your tenets and doctrines, you can earn shards of piety.
A great way to improve your character's piety is to apply one of the principles listed on the Faith page. These are clearly listed on the Faith page so that you can have a positive impact on your character. Some of them are also available on the decisions page. A good thing is that your character undergoes a pilgrimage. This makes your leader leave for a few months to visit one of the sacred places of your faith, encouraging him to come closer to his god (s). You cannot do this when your leader is at war or leading an army.
Similar to Prestige, your best bet is for random events to occur in the game. Read through the options and individual choices to choose those that allow your character to gain piety over prestige or currency. Be on the lookout for them in your game, and you might find ways to progress steadily through the devotion levels. Those who show themselves to be sufficiently devoted to their faith can create a new faith which is a different branch from this one, with various doctrines and principles, which sometimes facilitates succession.
