Inner emptiness means to be normal, to have a mind that is not scattered and confused. Anyone who experiences this really likes it. If it develops to its greatest degree, which is to be empty of egoism, then it is Nibbana.
In any religion there is the exoteric side — the tradition and forms, scriptures, ceremonies and disciplines—and the esoteric, which is the essential nature of that. So, in much of what we call religion, the emphasis is really on the external form.