What's "sweet god" mean and when do people say it?

Native speaker’s answer
Rebecca
"Sweet god" or the alternative, "sweet Jesus" is an informal exclamation to express alarm, anger, amazement, or exasperation. It could be considered blasphemy to some people! It's kind of like saying "oh my god" or "god," but adding "sweet" has a little different emphasis. As slang, I'd say "sweet Jesus" is more common than "sweet god." Ex: Oh, sweet Jesus! You scared me. Ex: Oh my god, this movie is going to be good. = Sweet god, this movie is going to be good.