What renews Nicks faith in Gatsby?

Gatsby admits that he can't really call himself an Oxford man because he only stayed for five months. This addmission helps clear up things Nick was unsure about.

“It was in nineteen-nineteen, I only stayed five months. That’s why I can’t really call myself an Oxford man.”

Tom glanced around to see if we mirrored his unbelief. But we were all looking at Gatsby.

“It was an opportunity they gave to some of the officers after the Armistice,” he continued. “We could go to any of the universities in England or France.”

I wanted to get up and slap him on the back. I had one of those renewals of complete faith in him that I’d experienced before.