What is the meaning of "so help me" in this passage from The Great Gatsby?
"'Let the bastards come in here if they want you, Rosy, but don't you, so help me, move outside this room.'"
1) no matter what
2) on my honour
3) something else?
This scene is a recollection by Wolfshiem, who has been involved in the bootlegging business for many years. When he meets Nick with Gatsby, Wolfshiem remembers when he met with associates at a restaurant and one of them was killed in a gang shooting. Wolfshiem's memory is good, and he infuses the retelling with drama:
"The old Metropole[...] I can't forget so long as I live the night they shot Rosy Rosenthal there. It was six of us at the table[...] the waiter came up to him with a funny look and says somebody wants to speak to him outside. 'All right,' says Rosy and begins to get up and I pulled him down in his chair.
" 'Let the bastards come in here if they want you, Rosy, but don't you, so help me, move outside this room.'
(Fitzgerald, The Great Gatsby, gutenberg.net.au)
The phrase "so help me," in this context, is not quite the same as the classic oath "so help you/me God." While the ordinary phrasing is meant to call on a higher power to hold a person to their word, it doesn't seem that Wolfshiem would be responsible for Rosy's fate. While the less-common (1) above: "no matter what," is possible, Wolfhiem knows that Rosy is likely to be killed, and sending the waiter over is just a ploy to get his guard down. In this context, Wolfshiem's comment could be parsed as follows:
"...don't you, [I mean this, and may God hold me accountable if I am lying], move outside this room."
In other words, Wolfshiem is adding gravity to his conviction by invoking God as a witness of his honesty.