Where did you read this, Frank? It's astonishing, so I had to look it up, and I see it attributed to George Denison Prentice (1859) in a scientific quotation book and several other books. I see it attributed to Pope in motivational quotation books and other areas.
And it doesn't sound like Pope, does it?
I got it A-Z Quotes. I assumed it was from one of Pope’s letters.