Why is there a difference between an Offence and a Blasphemy?

An offense is an act that is not approved of.

Blasphemy is disrespect of something that is considered sacred.

A blasphemy was, as had been impressed upon me often enough, a frightful thing.

Usually there was only some small thing wrong, but however much or little was wrong it was an Offence, and if it happened among people it was a Blasphemy — at least, that was the technical term, though commonly both kinds were called Deviations.