sole, soul

Sole or sole means the one and only--
The old woman's son was her sole means of support.
The error in his resume was the sole reason they didn't hire him.

Sole also means part of the bottom of a foot or shoe  ( the part that's not the heel )--
The shoe repair shop can fix your sole.
He got a blister on the sole of his foot.

Sole is also a kind of fish--
We had broiled sole for dinner.
Sole in butter is one of my favorites.

Soul or soul ( rhymes with sole ) means the seat of belief--to many people, the spirit of a person--
Many people believed that he sold his soul to the devil.
Some people believe the soul is immortal.

Now that you know that, you can say--
"Religious teaching is the sole reason some people believe they have a soul."

Note--"sold" is the past tense ( yesterday, or some time ago) form of "sell"--
Someone sold him the item on the internet. Then he resold it.
"Soled" is the past tense of "sole", meaning to put new soles on shoes, often called "resoled"--
The shoe repair shop soled my shoes.
I had my shoes resoled at the shoe repair shop.