This does not refer to a specific person. It refers to anyone who reads it aloud. Alternate translation: "anyone who reads aloud" (See: [[rc://en/ta/man/jit/figs-genericnoun]])
This can be stated in active form. Alternate translation: "obey what John has written in it" or "obey what they read in it" (See: [[rc://en/ta/man/jit/figs-activepassive]])