These words are spoken by Mephistopheles, a prince of the underworld who becomes Faustus' servant for twenty-four years after he sells his soul to Lucifer in exchange for unlimited power.
This passage appears in Act 5, Scene 1, where an Old Man appears in front of Faustus an calls him to renounce sourcery and repent, for is not to late to be saved. But Faustus sends him away, and when Mephistopheles appears, he asks the demon to torture the Old Man for offending him.
To this, Mephistopheles responds with these words, meaning that the torture will only be physical, since he cannot touch the man's soul.
a faux pas an embarrassing or tactless act or remark in a social situation.
a synonym for faux pas would be mistake, blunder, blooper, indiscretion, etc.
Background information in the exposition is the answer
The poem’s theme can be: sometimes harsh losses can cause one to see life differently, as a result of an overwhelming sense of grief.
