Just for the sake of qwerty I’ll try to explain the Atzmus thing in simple terms. If you learn Tanya perek 6, it says that only something which is nullified/ batul, to Hashem can become included the category of kedusha. Chassidus teaches that Hashem Echad means that everything should realize that its true self and existence is from Hashem/ one with Hashem. The more batul and humble a person lives, the more kedusha they can channel. The Gemara also says that Hashem can’t a dwell with an arrogant person. Chassidus takes it further that there is no other existence other than Hashem (all of creation is Hashem’s speech which is one with Him from His perspective, so we just need to realize this and love this way.)
So, someone like a true Rebbe can even channel Atzmus- a person can sense this kedusha when they interact with the tzadik who has converted his yetzer hara to be another positive force (Dovid hamelech did this, and anyone who is a tzadik gamur of Tanya can too.) Really, the true existence of every yid is actually one with Hashem’s Essence, which is why we won’t have an identity crisis when Hashem is revealed by geula, whereas goyim will.
Obviously, a”z can’t come in the picture here, because if someone speaks from their own ego etc, they’re not channeling any kedusha in that moment. What’s more, they’re clearly not what Chabad would consider a Rebbe, Rosh Bnei Yisrael, because they still have unpolished yeshus/ yetzer hara to deal with.