Besides tempo, at Bach's time, dynamics (loudness) weren't usually written down. But there's always a lot of interpretation involved, even today. The score is

Besides tempo, at Bach's time, dynamics (loudness) weren't usually written down. But there's always a lot of interpretation involved, even today. The score is a very rough model of the music, akin to jotted down notes outlining a novel. Or like a manuscript for a film.