What is an Establishment of Religion‪?‬

Excerpted from Antidisestablishmentarianism -- 
Hint. It's not what you think. It's a recipe for persecution, corruption and heresy. America's founding fathers understood that government must protect freedom, including the freedom to practice all religions. But they also understood that not all religions teach men how to be good citizens and make their countries prosper. The truth isn't out there somewhere, unfindable and unknowable. It's right here.