Galadriel: [deep, booming voice] YOU HAVE NO POWER HERE, SERVANT OF MORGOTH! YOU ARE NAMELESS, FACELESS, FORMLESS! GO BACK TO THE VOID FROM WHENCE YOU CAME!
The first thing she does is "put him in his place" by naming his superior. It's like calling customer service and asking for the manager when the employee is being stubborn haha. There is a great difference between being called a master or a servant. Being the servant reminds one subconsciously of their place of servitude, which can 'soften' them.
One reason to study the hierarchy of beings (in the real world) is so that you can properly name and identify entities, negative or positive. Or at least narrow it down.
In order for anything in physical creation to maintain itself, it needs three characteristics. Father, Son, Holy Spirit. Crone, Mother, Daughter. Shiva, Brahma, Vishnu. In alchemy, it is the Mercury, Sulphur and Salt (Spirit, Soul and Body).
When Galadriel revokes Sauron's Name, Face (the image in which he was created, similar to his Soul), and Form, she is revoking that which is the foundation of his being. She is using the Light to undermine these fundamental forces
And to further send him back to the void! The void is the place of potential and possibility, but of no action
on account of having no substance to act with. The void is the place where creation happens, but is not the cause of creation.
The most important part is the force behind the words, which in the movie is held in the vial during the banishing (the light) and what she acts through
. "The light shineth in the darkness, and the darkness comprehended it not."
In order for any banishing of negativity to be effective, a connection to the Light is necessary.