It is an organ tablature.
Organs don't have strings, therefore you don't have lines to represent them.
Wether or not you understand them is irrelevant. Point being, Bach was familiar with quick notation systems out of standard, that put the physical elements of the instrument beyond theory correct notation.
If so inclined, you can look for examples of Bach's work written in lute tablature, which may look more familiar to you.
Organs don't have strings, therefore you don't have lines to represent them.
Wether or not you understand them is irrelevant. Point being, Bach was familiar with quick notation systems out of standard, that put the physical elements of the instrument beyond theory correct notation.
If so inclined, you can look for examples of Bach's work written in lute tablature, which may look more familiar to you.
This isn't tab. Tab is numbers on lines to tell the user where to put his finger on the strings of the instrument. That has no relation at all to what Bach did here. Besides, if you are arguably the greatest composer of your time, you can pretty much do whatever you want.