What does Piety on Characters do?

[Saint Lucifer]

I have trouble understanding the Piety System.
So far I understood that the Item "Pure Thoughts" is an Ideology (like Rebellion or Cultist). Unlike the others, this ideology can not be upgraded with copies via the Headless Dragons, but solely via Me-Thinks after collecting 3 Piety points on it.
The item can gain Piety points from various events. Involving Characters with Piety seem to have no influence on the gain.
So, what i don't understand is: What are the Piety points on Characters for? Is there any effect when accumulating Piety on a Character?
Also, sometimes when recruiting a new Character, this Ideology can be placed and the Character will gain +1 Piety. Does doing so have any benefit?

[tpalnm]

You can collect all your follower's piety to upgrade "Pure Thoughts".

[Losk Osmanthus 路渐秋凉]

I only see huge investment...to start, need 3 piety and spend three >5 social characters for 3 days just to gather followers? This is nut. I did it though and had to do emergency sultan card swap...didn't see any immediate benefit.

Invest wisely.