I think people refer you to others who know more than them to explain why davka the term atzmus umehus, or how Hashem is mislabesh in the Rebbe etc.
But the simple meaning is pretty straightforward. The Rebbe is saying that when you ask the Rebbe you’re not asking the Rebbe as a person to go to Hashem for you necessarily, rather you’re asking Hashem as He is revealed through the Rebbe, like a Malach is called by Hashem’s Name when he is on a mission from Hashem, or like Moshe Rabbeinu who said “I will give grass “. The “I “ wasn’t Moshe speaking as a human being, although he was, it was Hashem speaking through Moshe because He was revealed in him.