This word shows that the author has stopped describing the action and is about to give background information before continuing the story. You should translate using the way your language introduces background information. (See: [[rc://en/ta/man/jit/writing-background]])
The phrase "put it into the heart" is an idiom that means to cause someone to think about something. Alternate translation: "the devil had already caused Judas Iscariot, the son of Simon, to think about betraying Jesus" (See: [[rc://en/ta/man/jit/figs-idiom]])