What will never be opened?
Rashi citing Tamid 30b: There were two Pishpeshim (small openings) to the main gate (of the Heichal), one to the north and one to the south. The southern one will never be opened.
Radak: The simple meaning is the gate of the Heichal.
Malbim: This gate (the eastern gate of Chatzer ha'Chitzonah. Also the eastern gate of Chatzer ha'Penimi will be closed weekdays, but that gate will be open on Shabbos and Yamim Tovim.) This gate will always be closed.
Since the gate will always be closed, why must the verse teach that no man will enter through it?
Malbim: One will not even enter its interior, not via the cells outside, nor via the Ulam inside.
When does Hashem come through the gate?
Rashi: He will come in the future. Radak ? i.e. His honor will come, like it says above (43:2).
What is the significance of the gate being permanently closed?
Malbim: This shows that the Shechinah will never leave there.
