I would describe Prelude in C as having one of the highest “simplicity to depth” ratios of any piece I’ve played. I wonder if anyone else has any they’d suggest as being incredibly simple while also being incredibly deep. (I get this is pretty subjective but I think you know what I mean)

I picked up a collection of several hundred of his 4-part chorales. I like to flip through the pages and pick one seemingly at random and play it. While some hit me harder than others, nearly all of them express this "simplicity to depth" ratio.

My latest favorite: Oh God, Hear My Sighs: https://soundcloud.com/nick66/oh-god-hear-my-sighs-bach