Why does it say "Midaber"?
Rashi: This is like Misdaber (Radak ? the Dagesh in the Beis is in place of the Sav.) This is for Hashem's honor. He spoke to Himself, and the voice came to Yechezkel.
Malbim: Until now, he received the influence of Nevu'ah via the angel holding the measuring rod. Now he [and the angel by him] heard Hashem speak to him from the Bayis, like "va'Yishma Es ha'Kol Midaber Elav? mi'Bein Shnei ha'Keruvim" (Bamidbar 7:89)
Why does it say "meha'Bayis"?
Radak: The honor was in the Bayis. I was in Chatzer ha'Penimi; the voice came to me.
Who was this man?
Radak #1: It is the man who appeared like Nechoshes (1:7).
Radak #2: It was a different angel.
Why did he stand by Yechezkel?
Malbim: He did not enter Kodesh ha'Kodoshim, the place of the honor.