From you post re: the word “religion”
In the context it was used back in the day, it was referring to separate Christian denominations. They were called “religions” back then.
One reason for that clause was because a certain denomination wanted to be the OFFICIAL “religion” (denomination) of the United States.
Back then the majority of people here were Christians of different denominations.
They were fleeing the religious persecution prevalent in Europe at that time.
“The legitimate powers of government extend to such acts only as are injurious to others. But it does me no injury for my neighbor to say there are twenty gods or no gods. It neither picks my pocket nor breaks my leg.”
Thomas Jefferson 1779